add vr_draw_ui method and make ui observer as method to be wildly available

src/app_events.cpp

@@ -30,6 +30,7 @@ void App::tick(float dt)
 
 void App::resize(float w, float h)
 {
+    LOG("App::resize %d %d", (int)w, (int)h);
     uirtt.create(w, h);
     redraw = true;
     width = w;