Allow multiple leaderboards and user stats depend upon game mods

[mellowagain]

trafficstars

Issue ported from osunavisu/kaede#2, originally created by @jacksonisiah

As seen on many other private servers, some mods are ranked but have a different leaderboards from others for game mods such as Relax or Auto Pilot.

These additionally require users to have separate stats for these game mods.