add messagebox to template binding, add absolute positioning layout, add observer instead of stack based node traversal which is not great in case of hierarchical traversal

engine/app.h

@@ -11,6 +11,7 @@ class App
     Sampler sampler;
     Texture2D tex;
     LayoutManager layout;
+    NodeMessageBox* msgbox;
     const uint16_t main_id = const_hash("main");
 public:
     static App I;