Osu: Non-ranked map disclaimer

[Craftplacer]

Describe the missing feature:
osu!stable warns the player that a map isn't ranked. osu!lazer should probably reimplement this. The warning should only appear inside PlayerLoader (or as another form), since if you skip a map in stable the warning is still visible, interferring with gameplay.

Proposal designs of the feature:

I would take care of this issue as a PR, if the design is set.

[peppy]

I think this would create more confusion than anything if implemented before score submission itself was.