Add a client for the MediaBrowserService.

1. Add a simple UI that shows
  a) using MediaBrowser to connect/browse to a MediaBrowserService exported by the same app.
  b) Use the MediaController callbacks to show and list the QueueItem objects.
2. Update the MusicService to add the activeQueueItemId to the PlaybackState.Builder. This
is used for marking/selecting the item being played.

Change-Id: I33b18804b571cd6e46f3f56bb534aa8b831e8acb