Add fake downtime period for årskravet

As memberservice don't want members to write data to Focus during their
årskrav process, we'll have to disable the entire user page.

Note that we could have just disabled the account form so that only
reads are avilable, instead of disabling both the user page, enrollment
and fjelltreffen, but instead of notifying us ahead of time, they
notified us when the disable was *urgent*, hence we'll fall back to this
quicker way of disabling the entire user page.