Fix issues with starting from an invalid state.

Starting with an empty collection caused the code to
crash. Fix that, and also upgrade the SDK to KitKat
since it's what I'll be using now.
Transparent icon that looks better on KitKat.
Use MediaPlayer.setNextMediaPlayer().

Try to make transitions less abrupt, something that has
been happening on my phone. Should probably also extend
this to transitions to different albums, but I need to
clean up this code before doing that.

There's probably a narrow race while setting up the next
track with a really slow phone and a short current track,
but that shouldn't be a problem in reality.