[examples] Add a Notebook case
[examples] Add a Notebook case

Embedding a Stage inside a notebook leads to interesting results:

  - if you call clutter_actor_show() on the embedded stage
    you'll probably get an unembedded stage
  - you might get small artifacts

Let's update the gtk-clutter-multistage example by adding Notebook
and embedding three stages inside two different pages.

Distrotech/clutter-gtk,Distrotech/clutter-gtk,Distrotech/clutter-gtk,GNOME/clutter-gtk,GNOME/clutter-gtk