Make i3 compatible with the very latest xcb

This involves:
 • Compiling with xcb-util instead of xcb-{atom,aux} (they merged the libraries)
 • Not using xcb-{event,property} anymore (code removed upstream)
 • Not using the predefined WINDOW, CARDINEL, … atoms (removed upstream)
 • Using the new xcb_icccm_* data types/functions instead of just xcb_*
   (for example xcb_icccm_get_wm_hints instead of xcb_get_wm_hints)

Also I refactored the atoms to use x-macros.

src/window.c

@@ -136,7 +136,7 @@ void window_update_transient_for(i3Window *win, xcb_get_property_reply_t *prop)
     }
 
     xcb_window_t transient_for;
-    if (!xcb_get_wm_transient_for_from_reply(&transient_for, prop))
+    if (!xcb_icccm_get_wm_transient_for_from_reply(&transient_for, prop))
         return;
 
     DLOG("Transient for changed to %08x\n", transient_for);