This enables me to set a ban expiry time for a user (manually, in the
database). By doing so:
* The user's page will say that they're temporarily banned, and show the
date their ban will be lifted.
* If the user tries to log in, it will say they're temporarily banned,
and give a specific datetime that the ban will be lifted by.
* An hourly cronjob will lift any bans that have expired.
Deimos