Added scene related things

src/scene.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <memory>
+#include "scene_tree.h"
+#include "timeline.h"
+
+BEGIN_NAMESPACE
+
+struct scene {
+    scene();
+
+    std::shared_ptr<scene_tree> tree;
+    std::shared_ptr<timeline> animation;
+};
+
+END_NAMESPACE