Latest changes for Bluetooth Beam.

- Receive transfer notifications and status info from Bluetooth, to show
  progress using Notifications.
- Added power manager, to keep track of BT power state, and turn BT off
  if possible.

TODO:
- UI for failed operations (ie transfer failed, Bluetooth enable failed).
- Cleanup of transfer list
- Make sure BT doesn't connect to other peripherals or isn't connectable.

Change-Id: I31450f589bbaeb72ee8c450c5019f00f0190b7aa