Properly configure sauna.reload
Generic, event-like processing of user selection processing
Move subscription between timeslots atomically

For signup sheets that where the user can signup for one time slot at
most, this allows changing subscription to a different slot
directly.

The main advantage for the user is that this minimizes the risk of
ending up with no subscription when manually changing the timeslot. As
currently the user is required to cancel the current subscription, it
is possible that both the old and new timeslots fill up in the time it
takes to submit the subscription for either/both slots.

Also, this saves time as the user doesn't have to retype the
information needed for the signup.
Remove user from wait lists on subscription change

Hmmm, this really doesn't make sense. Why not just remove the user upon
signing up for the first slot?
Add link to return to signup sheet from @@show-reservations
WIP: update of CHANGES for release