As wayland-client.h and wayland-server.h can't be included together,
split the Wayland backend file into clutter-backend-wayland.h, which
only defines the types, and clutter-backend-wayland-priv.h, which
actually uses the Wayland client types.
Signed-off-by: Daniel Stone <daniel@fooishbar.org>
https://bugzilla.gnome.org/show_bug.cgi?id=692851
