This also adds countable private message notifications.
Use float types for chat overlay height
Also inverts logic
# Conflicts: # osu.Game.Rulesets.Mania/UI/ManiaRulesetContainer.cs # osu.Game.Rulesets.Osu.Tests/TestCaseSlider.cs
Also cleans up some weird code
also OsuSetting to GameSetting
Limited to (relatively) sane values until we eventually get around to adjusting UI to allow higher extermities.