Make i3 compatible with the very latest xcb

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.