Bluetooth: API change.

Split BluetoothDevice into BluetoothDevice and BluetoothAdapter.

BluetoothAdapter: Represents the local BT adapter. Operations on the local
                  adapter (start a scan, etc).
BluetoothDevice: Represents a remote BT device. Operations on remote devices
                 (pair, connect, etc).

IBluetoothDevice.aidl -> Bluetooth.aidl
BluetoothDeviceService.java -> BluetoothDeviceService.java

TODO:
Javadoc