This doesn't quite follow the outdated draft-barbato-avt-rtp-theora-01,
but keeps consistant with RFC 5215 (vorbis) and with the ffmpeg
implementation

This is a good example of how to use Mac native widgets (NSView) inside QtVLC
For some reason, this is broken on the main playlist, but it works great on the plugins dialog or the simple prefs/keys
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

Signed-off-by: Rafaël Carré <rafael.carre@gmail.com>

vlc_clone_detach() is less flexible but we never used that lost
flexibilty. However, it will simplify a later Windows fix as well as
safely exposing detached threads to plugins.

It might be a good idea to do the same on other platforms

Ref #3804

This rework includes:
   - activation with mouse move
   - transparency and fading out supported if the WM allows it
   - fsc no longer a child window
     (this latter point should work out the refresh problems
      often mentioned on Vista and Win7)

The possibility to trigger callbacks when changing preferences was removed
 lately. So this code is now useless.