Attempts to eliminate any confusion between OsuHitObject (raw, parsed hit objects) and HitObject (interface for game object types).
- Renamed "HitObject" interface to "GameObject", since these objects are specific to gameplay.
- Renamed "OsuHitObject" to "HitObject", since these objects are primarily containers for parsed data.
Sorry if the name-swapping is confusing; these should be better names in the long run.
Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>