* Proper framebuffer refresh implementation.
  Limit update_session_views to the specified buffer rectangle.
* Advanced view stacking (moving other alien view behind stacked view)
* Prevent stack overflow by too deep recursion (too many views in the view stack)
  Idea: Dimension stack size for the worst case - max. recursion depth is
  max(screen width, screen height) if each view overlaps its next view in
  a way that one row/column is revealed.
