Adding delegate

Hi,

I added delegate for this controller, and those functions:

- (void) audioPlayer:(MDAudioPlayerController*)player
     didBeginPlaying:(MDAudioFile*)audio;
- (void) audioPlayer:(MDAudioPlayerController*)player
      didStopPlaying:(MDAudioFile*)audio;
- (void) audioPlayerDidClose:(MDAudioPlayerController*)player;

Please ask me if you have any question.

Signed-off-by: shyeon.kim <shyeon.kim@scipi.net>