mod_muc_moderation: Stamp XEP-0421 occupant-id for the acting moderator Gives clients some hint about which moderator it was who did the deed. The @by attribute does have the nick of the actor, but they could change their nickname at some point, which is what occupant-id solves. Ref #1816

This module discards typing notifications sent to a bare host JID,
preventing error replies to be sent. These errors are harmless but can
be annoying sometimes if your client shows them prominently.