Refactor CameraManager.

1. CameraManager should be the only class accessing android.hardware.Camera.
2. For potential future upgrade in Camera HAL and android.hardward.Camera API
   upgrade, CameraManager should be just an interface instead of concrete
   implementation.
3. waitDone() in CameraProxy is removed.
4. ShutterCallback, PreviewCallback, PictureCallback and AF Callbacks are
   wrapped by our own interfaces.

Change-Id: I595da17a1a9c6d476ee805b71c7f45ebb609e465