Merge branch 'master' into dev
PlayerController cleanup
PlayerController uses 2 MP threads for playback
first crossfading functionality (beta)
PlayerController cleanup
confusing pause button issues fixed
Bugfixes

Playback OnCompletion Issue fixed (playTrackPlaylist Method removed).
OnCompletionListener starts directly the prepareMediaPlayer method.

IPlaylistObserver now changes the Play/Pause Icon on PlayerFragment,
too, if you touch an PlaylistItem in Playlist.
own solution for onCompletionListener implemented

Implementation for PlayerController
new BPM Pitch feature added

Now you can pitch the BPM Track selection for better control if you
want run faster or slower
Merge branch 'dev'