I should be able to roll back the entire history of my Space

(User Story, Closed -> Fixed, Priority: Critical, Test Status: No automated tests yet , Reported By Justin du Coeur, )
History
Summary: That is, from the History Summary I should be able to say "revert to this point".
Obviously, this should come with a huge "are you sure you want to do this?" confirmation.
Internally, this would build the SpaceState as of that moment and slam it back into place.
In principle, this should include reverting the Conversations and User Values, but it's not clear what's actually desireable. Might need some sort of flag for the user to choose.
This is lowish-priority because I don't expect it to happen due to mistakes -- this is more about recovering from deliberate vandalism.