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.

include/handlers.h

@@ -13,9 +13,24 @@
 
 #include <xcb/randr.h>
 
+extern int randr_base;
 
 void add_ignore_event(const int sequence);
 
+/**
+ * Takes an xcb_generic_event_t and calls the appropriate handler, based on the
+ * event type.
+ *
+ */
+void handle_event(int type, xcb_generic_event_t *event);
+
+/**
+ * Sets the appropriate atoms for the property handlers after the atoms were
+ * received from X11
+ *
+ */
+void property_handlers_init();
+
 /**
  * There was a key press. We compare this key code with our bindings table and
  * pass the bound action to parse_command().