Support _NET_WM_VISIBLE_NAME. As per specification this is necessary since we can display custom titles with title_format.

fixes #1872

include/ewmh.h

@@ -45,6 +45,12 @@ void ewmh_update_desktop_viewport(void);
  */
 void ewmh_update_active_window(xcb_window_t window);
 
+/**
+ * Updates _NET_WM_VISIBLE_NAME.
+ *
+ */
+void ewmh_update_visible_name(xcb_window_t window, const char *name);
+
 /**
  * Updates the _NET_CLIENT_LIST hint. Used for window listers.
  */