Rework of Galaxy S-style power widget

This is a complete reworking of the notification power widget. It now
supports unlimited buttons which are scrollable after 6, and also uses
a more standalone method of declaring itself, as the entire thing is
simply its own FrameLayout that has been reworked, and deals with its
broadcast receiving and setting observation internally.

This also required rework to libmedia to add the media playback buttons.
The rework that was done was the addition of two more message states,
MEDIA_PLAYBACK_STARTED and MEDIA_PLAYBACK_PAUSED, as well as broadcasting
those messages when they are thrown.

Change-Id: I591d474b903f807198929d2e136b91486a222720