also changed batch-commit of multiple sets to database.
This should avoid any potential issues with intertwined transactions on the same connection while still allowing higher throughput when importing.
Moves star difficulty calculation entry-point to Beatmap, and sets star difficulty at the correct place for song select to display.
Note that this is a very naive approach and will result in file access exceptions. This will be fixed in a further commit.
They can now only be instantiated from BeatmapDatabase and are abstract (to avoid misuse).
Adds base classes for difficulty calculations, hooks them up with carousel container, and adds a port of the osu difficulty calculator.
Also makes the connection private.
Also fixes the broken IPC condition
Moves import code to BeatmapDatabase.