Bug 5045498 Keep track of RemoteControlClient play state change time

Store the time at which a RemoteControlClient changes it playback
 state, and send that time to the IRemoteControlDisplay.
This change will enable displays to implement strategies such as
 timeouts (e.g. to not display transport controls for clients which have
 been paused or stopped for a certain amount of time).

Change-Id: I902882500565743d455d56f6000efaf612cbe0a9