Move scaling container to OsuGame so OsuGameBase doesn't apply UI scale
For all usages, it looks like this was unnecessary.
Allows for better testability.
Also cleans up some weird code
# Conflicts: # osu.Game/Beatmaps/Drawables/UpdateableBeatmapBackgroundSprite.cs # osu.Game/Graphics/Containers/LinkFlowContainer.cs
Fix files with upper-case extensions failing to import correctly