This adds a --enable-wayland-compositor configure option which will add
support for a ClutterWaylandSurface actor which can be used to aid in
writing Wayland compositors using Clutter by providing a ClutterActor to
represent Wayland client surfaces.

Notably this configure option isn't tied into any particular backend
since conceptually the compositor support can be used in conjunction
with any clutter backend that has corresponding Cogl support.

Reviewed-by: Emmanuele Bassi <ebassi@linux.intel.com>