Add a "Date" variable for Leaderboards

[prototype464]

Feature request

Short description

Small idea for the addition of [MA]date for Leaderboards which displays the date the current entry happened

[garbagemule]

At face value, this would be pretty easy to implement, but we can't talk about recording dates without displaying dates, and we can't talk about displaying dates without talking about date formatting, which unfortunately isn't something anyone can agree on, which means we can only really hardcode a format, or we'll need to rework the leaderboards. The only reasonable format to use as a "standard" would be ISO 8601, specifically the YYYY-MM-DD variant, but it might not be familiar to players, so it could perhaps result in confusion.

If YYYY-MM-DD is good enough, I think we can introduce it, but I think I would prefer to find a way to make way for "real" leaderboards to take over via MAStats and MAPlaceholders. Not sure exactly how far along we are on that front though.