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/xcb.h

@@ -44,32 +44,9 @@
                           XCB_EVENT_MASK_SUBSTRUCTURE_NOTIFY |   /* …subwindows get notifies */ \
                           XCB_EVENT_MASK_ENTER_WINDOW)           /* …user moves cursor inside our window */
 
-
-enum {
-    _NET_SUPPORTED = 0,
-    _NET_SUPPORTING_WM_CHECK,
-    _NET_WM_NAME,
-    _NET_WM_STATE_FULLSCREEN,
-    _NET_WM_STATE,
-    _NET_WM_WINDOW_TYPE,
-    _NET_WM_WINDOW_TYPE_DOCK,
-    _NET_WM_WINDOW_TYPE_DIALOG,
-    _NET_WM_WINDOW_TYPE_UTILITY,
-    _NET_WM_WINDOW_TYPE_TOOLBAR,
-    _NET_WM_WINDOW_TYPE_SPLASH,
-    _NET_WM_DESKTOP,
-    _NET_WM_STRUT_PARTIAL,
-    WM_PROTOCOLS,
-    WM_DELETE_WINDOW,
-    UTF8_STRING,
-    WM_STATE,
-    WM_CLIENT_LEADER,
-    _NET_CURRENT_DESKTOP,
-    _NET_ACTIVE_WINDOW,
-    _NET_WORKAREA,
-    WM_TAKE_FOCUS,
-    NUM_ATOMS
-};
+#define xmacro(atom) xcb_atom_t A_ ## atom;
+#include "atoms.xmacro"
+#undef xmacro
 
 extern unsigned int xcb_numlock_mask;