wip: Changes of the week

- Move engine to a different crate
- Add engine trait
- Refactor the rest of the codebase to work with these changes
- Add debug ui buffer, use it to finish imgui support

core/src/scene.rs

@@ -17,6 +17,8 @@ impl Scene {
     }
 }
 
+impl Scene {}
+
 impl AsRef<Scene> for Scene {
     fn as_ref(&self) -> &Scene {
         &self