Change charset for certain fields to utf8mb4

The underlying cause of #419 is the default utf8 collation in MySQL/MariaDB, which only supports the base plane of Unicode (\u0000-\uffff).  By changing the collation to utf8mb4_general_ci, stuff like ban reasons and profile text may have emoji and other non-base-plane Unicode.

The charset for playlist titles is NOT changed, and non-base-plane characters are replaced by question marks.  This is because switching to utf8mb4 would make the primary key too long.

lib/channel/playlist.js

@@ -1243,6 +1243,8 @@ PlaylistModule.prototype.handleClonePlaylist = function (user, data) {
         });
     }
 
+    data.name = data.name.replace(/[^\u0000-\uffff]/g, "?");
+
     var pl = this.items.toArray();
     var self = this;
     db.saveUserPlaylist(pl, user.getName(), data.name, function (err) {