Update .gitignore
wayland: generalize ShellSurface to SurfaceExtension

We want to implement new shells and new extension interfaces
for wl_surface, so generalize the book-keeping structures.

https://bugzilla.gnome.org/show_bug.cgi?id=707128
wayland: split headers and distribute structure definitions

Instead of having all structures in one huge headers, move them
in the appropriate place, and create one header for surface state.

https://bugzilla.gnome.org/show_bug.cgi?id=707128
Move surface state tracking and surface interface to a separate file

Move everything surface related from meta-wayland.c to meta-wayland-surface.c

https://bugzilla.gnome.org/show_bug.cgi?id=707128
Add a private gtk-mutter protocol

Add a new interface, gtk_shell, than can be used by gtk to
retrieve a surface extension called gtk_surface, which will be
used to communicate with mutter all the GTK extensions to EWMH

https://bugzilla.gnome.org/show_bug.cgi?id=707128

Add support for GTK application menus

To do so, we need to be able to set surface state before creating
the MetaWindow, so we introduce MetaWaylandSurfaceInitialState as
a staging area.
The gtk-shell-surface implementation would either write to the
initial state, or directly to the window.

At the same, implement set_title and set_class too, because it's
easy enough.

https://bugzilla.gnome.org/show_bug.cgi?id=707128