Add a notification to the group edit page if any player has already played this music at camp

[duhiga]

It is nice to know from the admin page if any specific player has played the music before this camp. Suggested, create an AJAX call whenever the music dropdown is changed to get the list of players that have played this music before. Then if any match, have javascript create a red alert next to the player name if thy are selected in the player edit UI below.