Removed singleton logic from _ApplicationLogic since apparently it's not needed. Also deleted the _ApplicationLogic prefab. Whatever tutorial I followed to use that technique must have been for an old version of Unity or something.

Deleted Prefabs folder and moved levels/ball prefabs to Resources folder.

Deleted LevelN.cs scripts as they were not necessary. Public fields are defined in the BaseLevel.cs script attached to the LevelN prefabs and the values are set in the inspector.