Make a function to access overlay cells Closes #35.

gui/main_ui.cpp

@@ -53,6 +53,11 @@ namespace gui {
     $overlay_ui.show_sprite("middle", "blood_splatter");
   }
 
+
+  lel::Cell MainUI::overlay_cell(const std::string& name) {
+    return $overlay_ui.$gui.cell_for(name);
+  }
+
   bool MainUI::play_rotate() {
     bool done = $camera.play_rotate();
     $needs_render = !done;