Fix bugs in play status and play pos notifications

Fix multiple issues with status notificatios:
  * Playback state was not being sent when state wasn't sent
    accompanying a metadata change
  * Play state was being sent without an update
  * Position was being sent without a change and with the wrong
    indicator
  * Position was not being scheduled for update when playing.
  * Position was being scheduled for update when paused / stopped.

Bug: 30459664
Bug: 29400658
Bug: 28639383
Change-Id: Ic550dcab0430be45187b0267cc77875740388a2a