wayland: implement resizing and maximization for wayland clients

To properly resize clients, we need to send them configure events
with the size we computed from the constraint system, and
then check if the new size they ask is compatible with
our expectation.

Note that this does not handle interactive resizing yet, it
merely makes the API calls work for wayland clients.

https://bugzilla.gnome.org/show_bug.cgi?id=707401

src/core/constraints.h

@@ -35,7 +35,8 @@ typedef enum
   META_DO_GRAVITY_ADJUST    = 1 << 1,
   META_IS_USER_ACTION       = 1 << 2,
   META_IS_MOVE_ACTION       = 1 << 3,
-  META_IS_RESIZE_ACTION     = 1 << 4
+  META_IS_RESIZE_ACTION     = 1 << 4,
+  META_IS_WAYLAND_RESIZE    = 1 << 5
 } MetaMoveResizeFlags;
 
 void meta_window_constrain (MetaWindow          *window,