Tidy up osu-stable import process
Improves performance substantially.
Disable track changing buttons in the music controller depending on the current screen
FirstOrDefault when called on a TableQuery with a predicate doesn't use table indices
Now can locate any osu-stable installation using registry lookup (with ample fallbacks). Also uses a much more controlled access method via StableStorage.
Hide the notification overlay on screens which explicitly hide overlays
Hide Notification Overlay when playing osu
Reset carousel position when mouse leaves the carousel area
Store filenames against BeatmapSetFileInfo for correctness
Guarantees that backing files are cleaned up correctly. Also handles lingering "beatmaps" directory from older builds.
Beatmap import support from osu!stable
Also simplify initial migration for BeatmapStore by just nuking everything.
This fixes incorrect reference counts causing database desync.
Improvements to (progress) notifications
Fix cross-thread notification posting causing a hard crash
Make OsuButtons visually disable when not enabled