* Rename ShellGtkWindowActor to ShellGtkEmbed, and make it require
a ShellEmbeddedWindow rather than a general GtkWindow.
* Add ShellEmbeddedWindow subclass of GtkWindow that bypasses most
of the GtkWindow complexity for size negotiation, and calls out
to a clutter actor instead; also automatically handle reparenting
the GtkWindow into the stage window.
* Use the reworked ShellGtkEmbed in ShellTrayManager, this simplifies
the code a bit, and more importantly results in the tray icons
having the correct size negotiation, rather than having a fixed
24x24 size.
http://bugzilla.gnome.org/show_bug.cgi?id=580047
