[URGENT] [TBR] Restructure concert schema

- Add hasTimes field to concerts in the JSON schema
- Adds begins field to songs in the JSON schema
- Shows these times in the frontend
- Shows a warning message about the concert cancelation and the virtual
  concert planing
- Add CLI tool to get songs by person (tools/list.php)

Change-Id: Iec80ceb69e1a45cd467aaeaa59337a9966c78b7c
diff --git a/concerts/nadal2020nens.json b/concerts/nadal2020nens.json
index 7f11ce4..9b21169 100644
--- a/concerts/nadal2020nens.json
+++ b/concerts/nadal2020nens.json
@@ -1,12 +1,14 @@
 {
   "title": "Concert de Nadal 2020",
   "subtitle": "Nens i nenes",
-  "begins": 1608571800,
+  "begins": 0,
   "ends": 1608598800,
+  "hasTimes": true,
   "songs": [
     {
       "title": "Que tinguis un bon Nadal",
       "author": "Nadala popular anglesa",
+      "begins": 17.5,
       "performers": [
         {
           "instrument": "Veus i percussió",
@@ -25,6 +27,7 @@
     {
       "title": "Minuet en Sol major",
       "author": "Johann Sebastian Bach",
+      "begins": 17.5,
       "performers": [
         {
           "instrument": "Piano",
@@ -35,6 +38,7 @@
     {
       "title": "Bailes",
       "author": "Lamote de Grignon",
+      "begins": 19.5,
       "performers": [
         {
           "instrument": "Piano",
@@ -45,6 +49,7 @@
     {
       "title": "Campana del campanar",
       "author": "Nadala popular",
+      "begins": 18.5,
       "performers": [
         {
           "instrument": "Veus i percussió",
@@ -59,6 +64,7 @@
     {
       "title": "Chandelier",
       "author": "Sia",
+      "begins": 17.5,
       "performers": [
         {
           "instrument": "Veu",
@@ -73,6 +79,7 @@
     {
       "title": "Bohemian Rhapsody",
       "author": "Queen",
+      "begins": 18.5,
       "performers": [
         {
           "instrument": "Piano",
@@ -83,6 +90,7 @@
     {
       "title": "Oda a l'alegria",
       "author": "Ludwig van Beethoven",
+      "begins": 18.5,
       "performers": [
         {
           "instrument": "Piano",
@@ -93,6 +101,7 @@
     {
       "title": "El pastoret",
       "author": "Popular francesa",
+      "begins": 19.5,
       "performers": [
         {
           "instrument": "Piano",
@@ -103,6 +112,7 @@
     {
       "title": "Santa Nit",
       "author": "Franz Grüber",
+      "begins": 18.5,
       "performers": [
         {
           "instrument": "Guitarres",
@@ -129,6 +139,7 @@
     {
       "title": "Jingle Bells",
       "author": "Popular nordamericana",
+      "begins": 18.5,
       "performers": [
         {
           "instrument": "Piano",
@@ -139,6 +150,7 @@
     {
       "title": "Cançó de bressol",
       "author": "Johannes Brahms",
+      "begins": 18.5,
       "performers": [
         {
           "instrument": "Piano",
@@ -149,6 +161,7 @@
     {
       "title": "Dies d'alegria",
       "author": "Thord Gummesson",
+      "begins": 19.5,
       "performers": [
         {
           "instrument": "Veus",
@@ -167,6 +180,7 @@
     {
       "title": "Març",
       "author": "N. Baklanowa",
+      "begins": 18.5,
       "performers": [
         {
           "instrument": "Violí",
@@ -181,6 +195,7 @@
     {
       "title": "Serra que serra",
       "author": "Nadala popular catalana",
+      "begins": 19.5,
       "performers": [
         {
           "instrument": "Veus",
@@ -199,6 +214,7 @@
     {
       "title": "Mi burrito sabanero",
       "author": "Villancico colombiano",
+      "begins": 19.5,
       "performers": [
         {
           "instrument": "Saxo",
@@ -209,6 +225,7 @@
     {
       "title": "This House Is Not For Sale",
       "author": "Bon Jovi",
+      "begins": 19.5,
       "performers": [
         {
           "instrument": "Veu",
@@ -231,6 +248,7 @@
     {
       "title": "El noi de la mare",
       "author": "Popular catalana",
+      "begins": 17.5,
       "performers": [
         {
           "instrument": "Piano",
@@ -241,6 +259,7 @@
     {
       "title": "The pipers are coming",
       "author": "Johann Sebastian Bach",
+      "begins": 17.5,
       "performers": [
         {
           "instrument": "Piano",
@@ -255,6 +274,7 @@
     {
       "title": "La patinadora",
       "author": "J. Thompson",
+      "begins": 17.5,
       "performers": [
         {
           "instrument": "Piano",
@@ -269,6 +289,7 @@
     {
       "title": "Huahuanaca",
       "author": "Nadala popular boliviana",
+      "begins": 19.5,
       "performers": [
         {
           "instrument": "Veus",
@@ -295,6 +316,7 @@
     {
       "title": "Déjame",
       "author": "Los Secretos",
+      "begins": 19.5,
       "performers": [
         {
           "instrument": "Guitarres",
@@ -309,6 +331,7 @@
     {
       "title": "Oda a l'alegria",
       "author": "Ludwig van Beethoven",
+      "begins": 19.5,
       "performers": [
         {
           "instrument": "Piano",
@@ -317,18 +340,9 @@
       ]
     },
     {
-      "title": "Mad World",
-      "author": "Roland Orzabal",
-      "performers": [
-        {
-          "instrument": "Piano",
-          "names": ["Carlota Bou", "Marcela Bou"]
-        }
-      ]
-    },
-    {
       "title": "Minuet",
       "author": "C. Stamitz",
+      "begins": 19.5,
       "performers": [
         {
           "instrument": "Flauta travessera",
@@ -339,6 +353,7 @@
     {
       "title": "Récréation de la Flauta Màgica",
       "author": "W. A. Mozart",
+      "begins": 19.5,
       "performers": [
         {
           "instrument": "Flauta travessera",
@@ -349,6 +364,7 @@
     {
       "title": "All I Want for Christmas Is You",
       "author": "Mariah Carey",
+      "begins": 17.5,
       "performers": [
         {
           "instrument": "Veu",