Re-implement support for the urgency hint, extend t/13-urgent.t

The actual rendering will follow

include/data.h

@@ -272,6 +272,10 @@ struct Con {
 
     struct Window *window;
 
+    /* Should this container be marked urgent? This gets set when the window
+     * inside this container (if any) sets the urgency hint, for example. */
+    bool urgent;
+
     /* ids/gc for the frame window */
     xcb_window_t frame;
     xcb_gcontext_t gc;

include/handlers.h

@@ -171,12 +171,14 @@ int handle_normal_hints(void *data, xcb_connection_t *conn, uint8_t state,
                         xcb_window_t window, xcb_atom_t name,
                         xcb_get_property_reply_t *reply);
 
+#endif
 /**
  * Handles the WM_HINTS property for extracting the urgency state of the window.
  *
  */
 int handle_hints(void *data, xcb_connection_t *conn, uint8_t state, xcb_window_t window,
                   xcb_atom_t name, xcb_get_property_reply_t *reply);
+#if 0
 
 /**
  * Handles the transient for hints set by a window, signalizing that this

include/workspace.h

@@ -90,14 +90,16 @@ void workspace_unmap_clients(xcb_connection_t *conn, Workspace *u_ws);
  *
  */
 void workspace_map_clients(xcb_connection_t *conn, Workspace *ws);
+#endif
 
 /**
  * Goes through all clients on the given workspace and updates the workspace’s
  * urgent flag accordingly.
  *
  */
-void workspace_update_urgent_flag(Workspace *ws);
+void workspace_update_urgent_flag(Con *ws);
 
+#if 0
 /*
  * Returns the width of the workspace.
  *