separate global tick from draw so on tick any node can request a redraw

src/node.h

@@ -211,6 +211,7 @@ public:
     virtual void removed(Node* parent);
     const Node* init_template(const char* id);
     void tick(float dt);
+    void app_redraw();
     void async_start();
     void async_update();
     void async_end();