Fix crash on orientation change when volume panel is showing

- In volume panel do not post to handler when the panel is dismissed.
  Posting caused an "Activity has leaked window that was originally
  added ..." error in the log, and an "IllegalArgumentException: View
  not attached to window manager" exception when the dialog was closed
  by the message handler.
- In now playing fragment, do not post to the UI thread, when showing
  a volume message from LMS, as the volume panel internally does that.
- Correctly unregister the volume callback in onPause in the now
  playing fragment. Failing to do that, caused an exception when
  rotating the device for the second time, cause the no longer active
  fragment receives a volume message from the LMS, which is passed on
  to its volume panel. When the not activy volume panel receives a
  timeout, it gets an exception when trying to dismiss the dialog.

Signed-off-by: Kurt Aaholst <kaaholst@gmail.com>
ActionBarCompat: Support action bar items setEnabled/setVisibility

from onCreateOptionsMenu