Fixes #2151.
- removing unnecessary `using`s - name Fields/Methods according to rules - removing unnecessary initializations
Beatmap works, Storyboard not...
# Conflicts: # osu.Game.Rulesets.Mania/Objects/Drawables/DrawableHoldNote.cs # osu.Game.Rulesets.Mania/Objects/Drawables/DrawableManiaHitObject.cs