don't allow song-applied mods to persist

"Gimmick" songs designed for SM 3.95/OpenITG use GAMESTATE:ApplyGameCommand() to force modifiers during gameplay.  If the song ends and mods are still in effect, those mods persist.

This update saves a string of playeroptions on ScreenPlayerOption's OffCommand and applies those again upon reaching ScrenSelectMusic (this handles players completing a song or canceling out).