Update MIDIMusicPlayer.java

Ajout de SetVolume pour changer le volume de la musique de fond.
Update MP3MusicPlayer.java

Add SetVolume, but not yet implemented.
Update MusicPlayer.java

Add abstract method SetVolume().
Update WaitBackgroundRequestBehaviour.java

Add case CHANGE_VOLUME to modify the background music's volume.
Update BackgroundMusicData.java

Add data about music's volume to allow the modification of the background music volume.
FIX

SetVolume(int volume)
et import d'une lib pour le MIDI.
Merge pull request #52 from hukewei/alex

FIX
Merge branch 'master' into keweihu/test

Conflicts:
	src/fr/utc/leapband/sma/sound/MP3MusicPlayer.java