Allows you to create a nice music player with all the
trimmings, including:
* up to 5 actions in the bigContentView, styled as
transport control buttons
* up to 2 of those actions in the 1U (!)
* a nice custom progress bar
* a tinted background (taken from your Notification.color)
* a special place to put your MediaSessionToken
Bug: 15147533
Change-Id: Ic20a2b369eb6c5fe4853987a44ffd9bace720c7f
842dd77bb9