Make the transitions more solid by having an open/close set of functions to maintain cleaning up internal state.

gui/dnd_loot.hpp

@@ -39,6 +39,8 @@ namespace gui {
       void handle_mouse(Event ev, guecs::UI& gui);
       void mouse_action(bool hover);
       void render();
+      void open();
+      void close();
       sf::Vector2f mouse_position();
   };
 }