[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/nadal2020joves.json b/concerts/nadal2020joves.json
index 028488f..5481a8c 100644
--- a/concerts/nadal2020joves.json
+++ b/concerts/nadal2020joves.json
@@ -3,6 +3,7 @@
   "subtitle": "Joves i adults",
   "begins": 1608312600,
   "ends": 1608339600,
+  "hasTimes": false,
   "songs": [
     {
       "title": "Santa Nit",