Manual signup management capability for users with "manage signups" permission

[nbudin]

We'd deliberately left this out originally, on the principle that in a self-service signup convention, it was good not to even expose the ability for admins to mess with signups, in order to avoid even the possibility of abuse. But, with the SMS capability and the new never-freeze-the-site regime it enables, it seems more necessary to allow people at the Ops desk to make changes to users' signups without having to have the "become user" ability.

We already have manual signup management for moderated signup conventions, but the UI for it is a bit targeted at their use cases, and may or may not be able to be easily repurposed.

(cc @marleighnorton)

[marleighnorton]

I can see the potential for abuse, and respect that. Maybe it's just a thing that happens during the con? That's the main scenario I'm foreseeing here.

For future readers, the use case here is that during the con a player needs to withdraw and can't get to the website, such that someone else has to remove them on their behalf. Imagine something pressing comes up where the player tells the GM/posts to the FB group and then disappears.