Users now have a toggleable can_gamble setting which disables their
ability to use all chance-based gains on the site: viz. slots,
blackjack, the lottery, and treasure chests.
This only applies on invocation of commands that start gambling
games, so it should cause no bugs when toggled with e.g. active
blackjack games.
This was added for the benefit of users with actual problems with
gambling, be they past addiction or religious conviction. All future
gambling features are humbly requested to respect it.