Introducing Notification.MediaStyle.

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