AudioManager: Add Bluetooth A2DP profile trigger

    - Introduce a new profile trigger for Bluetooth A2DP
      connections.  We can't use the default ACTION_ACL_CONNECTED
      because it would apply the volume settings before routing
      has been established to the A2DP device.
    - Modify AudioService to send an intent after the audio
      route has changed to A2DP to ensure our volume change
      will apply to the correct device.
    - Allows the user to disable the A2DP profile and still
      trigger the profile change.

Fixes JIRA issue: BACON-47

Change-Id: Ib51dac6d79abbaf494b86af4480e293162814459