Store scores of unranked beatmaps

[Lekuruu]

Low priority for now, since this could break stuff easily if not implemented properly.

[mazziebot]

in what ways would this break for anyone else wanting to fix this themselves?

[Lekuruu]

I think the required checks for ranked/unranked Beatmaps are there for stats updates, although I would need to investigate that again.
BSS would also need to nuke all scores on an update, which it doesn't do right now if I recall.