Initial prototype
diff --git a/concerts/nadal2020joves.json b/concerts/nadal2020joves.json
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+{
+  "title": "Concert de Nadal 2020",
+  "subtitle": "Joves i adults",
+  "begins": 1608227730,
+  "songs": [
+    {
+      "title": "Santa Nit",
+      "author": "Franz Grüber",
+      "performers": [
+        {
+          "instrument": "Guitarres",
+          "names": ["Juan del Vas", "Elder Navarrete", "Marta Giménez", "Jesús Floro"]
+        },
+        {
+          "instrument": "Piano",
+          "names": ["Marcela Bou"]
+        }
+      ]
+    },
+    {
+      "title": "Shallow de \"A star is born\"",
+      "author": "Mark Ronson",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Jazmín tempo"]
+        }
+      ]
+    },
+    {
+      "title": "Minué en Sol Major",
+      "author": "Johann Sebastian Bach",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Laura Matencio"]
+        }
+      ]
+    },
+    {
+      "title": "Somewhere de \"West Side Story\"",
+      "author": "Leonard Bernstein",
+      "performers": [
+        {
+          "instrument": "Flauta travessera",
+          "names": ["Raquel Caballero"]
+        },
+        {
+          "instrument": "Piano",
+          "names": ["Carme Martínez"]
+        }
+      ]
+    },
+    {
+      "title": "Sargento de hierro",
+      "author": "Morgan",
+      "performers": [
+        {
+          "instrument": "Veu",
+          "names": ["Lucía Ariza"]
+        },
+        {
+          "instrument": "Piano",
+          "names": ["Tesi Osuna"]
+        }
+      ]
+    },
+    {
+      "title": "Déjame",
+      "author": "Los Secretos",
+      "performers": [
+        {
+          "instrument": "Guitarres",
+          "names": ["Jorge Sánchez", "Claudia Salvador", "Ester Sánchez", "Pablo Prieto", "Kilian Molina"]
+        },
+        {
+          "instrument": "Bateria",
+          "names": ["Xavi Martín"]
+        },
+        {
+          "instrument": "Baix",
+          "names": ["Xavi Sixto"]
+        }
+      ]
+    },
+    {
+      "title": "Fantasia Impromptu",
+      "author": "Frédéric Chopin",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Carmen Vilanova"]
+        }
+      ]
+    },
+    {
+      "title": "Allegro del concert en Si m Opus 35",
+      "author": "O. Rieding",
+      "performers": [
+        {
+          "instrument": "Violí",
+          "names": ["Raquel Xin López"]
+        },
+        {
+          "instrument": "Piano",
+          "names": ["Carme Martínez"]
+        }
+      ]
+    },
+    {
+      "title": "Sign of the Times",
+      "author": "Harry Styles",
+      "performers": [
+        {
+          "instrument": "Veu",
+          "names": ["Adrià Izquierdo"]
+        },
+        {
+          "instrument": "Piano",
+          "names": ["Laura Matencio"]
+        },
+        {
+          "instrument": "Guitarres",
+          "names": ["Alejandro Mora", "Pablo Jiménez"]
+        },
+        {
+          "instrument": "Bateria",
+          "names": ["Xavi Martín"]
+        }
+      ]
+    },
+    {
+      "title": "A Million Dreams",
+      "author": "The Greatest Showman",
+      "performers": [
+        {
+          "instrument": "Veu",
+          "names": ["Carmen Vilanova"]
+        },
+        {
+          "instrument": "Piano",
+          "names": ["Tesi Osuna"]
+        }
+      ]
+    },
+    {
+      "title": "Arrival of the birds",
+      "author": "The Cinematic Orchestra",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Javier Pérez"]
+        }
+      ]
+    },
+    {
+      "title": "Primer moviment Sonata Clar de Lluna",
+      "author": "Ludwig van Beethoven",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Cristina García"]
+        }
+      ]
+    },
+    {
+      "title": "Primer moviment Sonata Clar de Lluna",
+      "author": "Ludwig van Beethoven",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Cristina García"]
+        }
+      ]
+    },
+    {
+      "title": "Hawái",
+      "author": "Maluma",
+      "performers": [
+        {
+          "instrument": "Veu",
+          "names": ["Harrison Medina"]
+        },
+        {
+          "instrument": "Piano",
+          "names": ["Laura Matencio"]
+        },
+        {
+          "instrument": "Guitarres",
+          "names": ["Alejandro Mora", "Pablo Jiménez"]
+        },
+        {
+          "instrument": "Bateria",
+          "names": ["Xavi Martín"]
+        }
+      ]
+    },
+    {
+      "title": "Ain't no sunshine",
+      "author": "Bill Withers",
+      "performers": [
+        {
+          "instrument": "Guitarres",
+          "names": ["Luis Fernández", "Alejandro Mora", "Pablo Jiménez"]
+        },
+        {
+          "instrument": "Violins",
+          "names": ["Raquel Xin López", "Carmen Vilanova"]
+        },
+        {
+          "instrument": "Bateria",
+          "names": ["Xavi Martín"]
+        },
+        {
+          "instrument": "Baix",
+          "names": ["Gabriel Villalba"]
+        }
+      ]
+    },
+    {
+      "title": "Quan torna Nadal",
+      "author": "Popular nordamericana",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Nora Pulido", "Natalia Ying López"]
+        }
+      ]
+    },
+    {
+      "title": "Oda a l'alegria",
+      "author": "Ludwig van Beethoven",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Salma Nicole Padilla", "Marcel Tapiz"]
+        }
+      ]
+    },
+    {
+      "title": "Part-Time Lover",
+      "author": "Stevie Wonder (versió Operación Triunfo)",
+      "performers": [
+        {
+          "instrument": "Veu",
+          "names": ["Ester Sánchez"]
+        },
+        {
+          "instrument": "Piano",
+          "names": ["Laura Matencio"]
+        },
+        {
+          "instrument": "Guitarres",
+          "names": ["Alejandro Mora", "Pablo Jiménez"]
+        },
+        {
+          "instrument": "Bateria",
+          "names": ["Xavi Martín"]
+        }
+      ]
+    },
+    {
+      "title": "Oració al maig",
+      "author": "Eduard Toldrà",
+      "performers": [
+        {
+          "instrument": "Violí",
+          "names": ["Carmen Vilanova"]
+        },
+        {
+          "instrument": "Piano",
+          "names": ["Carme Martínez"]
+        }
+      ]
+    },
+    {
+      "title": "Suspicious Minds",
+      "author": "Elvis Presley",
+      "performers": [
+        {
+          "instrument": "Veu",
+          "names": ["Pol Espuny"]
+        },
+        {
+          "instrument": "Guitarres",
+          "names": ["Luís Fernández", "Alejandro Mora", "Pablo Jiménez"]
+        },
+        {
+          "instrument": "Bateria",
+          "names": ["Xavi Martín"]
+        },
+        {
+          "instrument": "Baix",
+          "names": ["Gabriel Villalba"]
+        }
+      ]
+    },
+    {
+      "title": "Minuetto en Sol Major",
+      "author": "Johann Sebastian Bach",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Natalia Ying López"]
+        }
+      ]
+    },
+    {
+      "title": "Happier",
+      "author": "Marshmello & Bastille",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Marc Lozano"]
+        }
+      ]
+    },
+    {
+      "title": "Swaying Silver Birches",
+      "author": "Charles Leslie",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Jaume Arnau"]
+        }
+      ]
+    },
+    {
+      "title": "Old McDonald",
+      "author": "Popular nordamericana",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Laura Matencio", "Justin Pastran"]
+        }
+      ]
+    },
+    {
+      "title": "I Don't Wanna Be You Anymore",
+      "author": "Billie Eilish",
+      "performers": [
+        {
+          "instrument": "Veu",
+          "names": ["Nora Pulido"]
+        },
+        {
+          "instrument": "Piano",
+          "names": ["Laura Matencio"]
+        },
+        {
+          "instrument": "Guitarres",
+          "names": ["Alejandro Mora", "Pablo Jiménez"]
+        },
+        {
+          "instrument": "Bateria",
+          "names": ["Xavi Martín"]
+        }
+      ]
+    },
+    {
+      "title": "Flora's secret",
+      "author": "Enya",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["David Solé"]
+        }
+      ]
+    },
+    {
+      "title": "7 Rings",
+      "author": "Ariana Grande",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Diego Castro"]
+        }
+      ]
+    },
+    {
+      "title": "Voy en un coche",
+      "author": "Cristina y los subterráneos (versió Operación Triunfo)",
+      "performers": [
+        {
+          "instrument": "Veu",
+          "names": ["Raquel Caballero"]
+        },
+        {
+          "instrument": "Guitarres",
+          "names": ["Alejandro Mora", "Pablo Jiménez"]
+        },
+        {
+          "instrument": "Bateria",
+          "names": ["Xavi Martín"]
+        }
+      ]
+    },
+    {
+      "title": "Just you and I",
+      "author": "Tom Walker",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Marcel Tapiz"]
+        }
+      ]
+    },
+    {
+      "title": "Mad World",
+      "author": "Roland Orzabal",
+      "performers": [
+        {
+          "instrument": "Piano",
+          "names": ["Marcela Bou", "Carlota Bou"]
+        }
+      ]
+    },
+    {
+      "title": "All I Want for Christmas Is You",
+      "author": "Mariah Carey",
+      "performers": [
+        {
+          "instrument": "Veu",
+          "names": ["Lucía Ariza", "Raquel Caballero", "Ester Sánchez", "Carmen Vilanova"]
+        },
+        {
+          "instrument": "Piano",
+          "names": ["Adrià Vilanova"]
+        },
+        {
+          "instrument": "Guitarres",
+          "names": ["Alejandro Mora", "Pablo Jiménez"]
+        },
+        {
+          "instrument": "Bateria",
+          "names": ["Xavi Martín"]
+        }
+      ]
+    }
+  ]
+}