Future idea: competitive leaderboards

[Artemis-the-gr8]

Set a scoreboard for a certain statistic from a certain point in time, to have a daily/weekly/monthly competition for this stat:

• [ ] select the stat to do this for, and for how long
• [ ] write every player's entry for this stat to a file
• [ ] upon leaderboard request, calculate how much they gained since this value was set
• [ ] display leaderboard with special title to indicate it's a temp competition