Made BeatButton easier to expand and modify.
Fixed a map bug, buttons now stay green until sound stops.

Added onCompletionListener to BeatButton.
Changed MediaPlayerThread to create new media player on instantiation
and on change of track.
Changed MediaPlayerManager to return the MPthread's media player for
BeatButton.
Now buttons stay green until the sound stops.
Merged Matt & Raj changes
Merged in MattTest Branch