modules: add android_window vout

 - used for direct and non direct rendering (replace opaque.c)

 - use nativewindowpriv: more control than the public api, since you can set
   orientation, crop, cancel a buffer without displaying it and allocate more
   than one buffers.

 - fallback to nativewindow if nativewindowpriv fails (with only one buffer in
   the pool then).

 - Only one way to display subtitles: use a seperate android surface.

 - Fix subtiles display in case or source aspect != 1.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>