Introduce 'shell' object for moving and resizing surfaces in the compositor

TODO

@@ -1,5 +1,13 @@
 Core wayland protocol
 
+ - enter notify needs coordinates for cases where pointer focus
+   changes without motion (surfaces coming or going)
+
+ - generate marshal stubs as static inline functions.
+
+ - don't store globals on client side, require global_handler like
+   everything else.
+
  - glyph cache
 
  - dnd, figure out large object transfer: through wayland protocol or