Implement resizing (still buggy)

Committing basic resizing functionality. We need testcases for the bugs and
then eliminate them.

include/resize.h

@@ -0,0 +1,6 @@
+#ifndef _RESIZE_H
+#define _RESIZE_H
+
+int resize_graphical_handler(Con *first, Con *second, orientation_t orientation, xcb_button_press_event_t *event);
+
+#endif