Implement saving of most played beatmap by user

[mellowagain]

Official osu!Bancho profiles have a "Most played beatmaps" section which contains beatmaps and their playcount for the individual user.

Quering this is already possible if a server has decided to set save failed scores in the scores table. However, Shiro should have this possibility without depending on a config value, so I propose the implementation of a new database table which saves this value.