Implement floating (please test and find bugs)

Details which are missing: A command to hide/show all floating clients,
moving/resizing clients with your mouse holding Mod1 (click anywhere
in the client, not just on its borders), resize/move by keyboard, select
next/previous client by keyboard

include/xcb.h

@@ -126,4 +126,10 @@ void fake_absolute_configure_notify(xcb_connection_t *conn, Client *client);
  */
 void xcb_get_numlock_mask(xcb_connection_t *conn);
 
+/**
+ * Raises the given window (typically client->frame) above all other windows
+ *
+ */
+void xcb_raise_window(xcb_connection_t *conn, xcb_window_t window);
+
 #endif