Fix the leaderboard

[CapOfCave]

Fix the leaderboard by accessing the database when the command is called.

Ideally, the members would be fetched lazily for performance reasons.

The DevDenPaginator can be reused for that.

[CapOfCave]

I self-assigned because I already did minor work on this. However, it looks like I might not be able to implement this feature in the near future, so if anybody wants to take it over, feel free to do so.