I need a way to ask if a cell exists for more dynamic layouts.

src/guecs/ui.cpp

@@ -51,6 +51,10 @@ namespace guecs {
     return $ents_name.at(gui_id);
   }
 
+  bool UI::contains(const string& name) {
+    return $name_ents.contains(name);
+  }
+
   Entity UI::entity(const string& name) {
     assert($name_ents.contains(name) &&
         "GUECS entity does not exist. Mispelled cell name?");