Remove FFMPEG layer from notification center on dealloc

- Notifications were being sent to it long after it was
  dead.
- This fixes the exceptions when hovering the mouse over
  the timeline slider.
Remove DisplayLink code from MMovieLayer_FFMPEG

- This code isn't being used anymore.
Remove GL texture creation from OSDs

- Not using OpenGL for display anymore.
Add the OSD "message" back

- This is the start of bringing back OSDs.
- It doesn't handle resizing of the view properly
  (i.e. it's not handled at all).