Track handling of space access updates

[adehnert]

We send CAC a lot of emails with updates to space access. Sometimes, I think some of them slip through the cracks. It would be awesome if the DB tracked each update email it send out and checked if CAC had replied yet, and somehow warned about possibly-unhandled requests. (Probably keeping a human in the loop, rather than directly notifying CAC.)

Also neat would be tracking response time, to get evidence that it has gotten much better (at least, that's my sense).