move platformes and scenery to /apps/demos/

apps/demos/scenery/scenes/scene.c

@@ -0,0 +1,8 @@
+#include "scene.h"
+#include "../state.h"
+
+
+void switch_to(State *state, Scene *(*scene_func)(State *)) {
+    state->next_scene = scene_func(state);
+    state->is_scene_switching = true;
+}