Fix TestCaseMultiScreen intermittent failures
Implement new difficulty calculator structure
# Conflicts: # osu.Game.Rulesets.Osu/Difficulty/OsuLegacyDifficultyCalculator.cs
Fix test dlls being loaded as actual rulesets (and failing)
Add "Grow" mod
Improve the build script (and move to a better location)
Add difficulty calculator tests
Fix nullref when entering multiplayer
Fix screen tests
Add support for the HitCircleOverlap property of legacy skins
Fix mouse cursor appearing prematurely during startup