Optimize GUECS a bit so that it automatically sets up the cell names and lel::Cell contents in the world, making it easier to work with.

guecs.cpp

@@ -12,6 +12,11 @@ namespace guecs {
   void UI::layout(std::string grid) {
     $grid = grid;
     $parser.parse($grid);
+
+    for(auto& [name, cell] : $parser.cells) {
+      auto ent = entity(name);
+      $world.set<lel::Cell>(ent, cell);
+    }
   }
 
   DinkyECS::Entity UI::entity(std::string name) {