Investigate whether there's a better way to do the recent scores lookup

[peppy]

The only reason for index KEY user_ruleset_id_index (user_id,ruleset_id,id DESC) existing is to do recent score display on user profiles.

Historically, we've maintained a separate table for this. We may just want to go back to doing this if it means the main table gets a whole lot smaller.

[peppy]

As per #17, we'll stick to this method for now (as the modified index does need to remain present).