MAP: Handle following in MAPS:

- Expose isMapStarted() API to maintain the Profile
  internal state and perform start/stop based on later.

- Track registration and unregistration for BluetoothMapAppObserver
  BroadcastReceiver through  a instance flag to avoid
  possible IntentReceiver leaks.

- Avoid MasInstance shutdown block to handle possible ANR.

- Other conditional checks to avoid possible NPE.

CRs-Fixed: 969230
Change-Id: I473f8ad8998a1bf7f2da3bcab2380ed0954ed8bc