Adds base classes for difficulty calculations, hooks them up with carousel container, and adds a port of the osu difficulty calculator.
- Applies to Slider Ticks and start circle. repeat/endpoints still need addressing. - Removed SliderTicksLayer abstraction for now.
Also adjusts tracking to only change during sldier active time.
Conflicts: osu.Game.Modes.Osu/Objects/Drawables/DrawableSlider.cs osu.Game.Modes.Osu/Objects/Slider.cs
# Conflicts: # osu.Game.Modes.Osu/Objects/Drawables/DrawableSlider.cs
Note, that circle sizes still are wrong compared to stable osu. In order to fix this, the base radius of hitcircles needs to become 64, but it currently is 72.