Topic lock sandbox

I've added some new functionality for myself (and the Shirrifs/moderators) to be able to close down threads that have gotten out of hand, either temporarily or permanently once we've discussed internally. The moderators can still reply to those threads so we can explain why it is locked, if needed.

Shirrifs, feel free to lock and unlock this, and try to reply to it, etc. You won't be able to see what it looks like locked to a normal user, but I will take screenshots from Ephemeral while it is locked for you.