Initital list selection

-Song notification in current playlist
-Change default action in current playlist to just play the selected song

Split the service callback interface int smaller parts, so activites can
subscribe to receive notifications for only events that are of interest.
Fixed bug in onMusicChanged in current playlist

On some platforms we get:
CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
So the onNotifyDaasetChanged is now called from the ui thread.
Refactor service callback interface, update current playlist as song changes.

Split out the "handshake completed" and "music changed" parts of the
service callback interface in to their own callbacks, so that activities
can receive notifications of just the events that they care about.

Track music changes in SqueezerCurrentPlaylistActivity, so that if the
current song changes while the activity is open the UI will update
accordingly.