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

Cargo.toml

@@ -5,5 +5,6 @@ members = [
     "platform",
     "asset",
     "game",
-    "ecs"
+    "ecs",
+    "engine"
 ]