Unidentified invitee timeouts

[redlizard]

Currently, no timeouts of any sort apply to unidentified invitees. This is not a huge problem as their participation is not required anywhere, but it does clog up the conversation state machine for no good reason.

There are two easy ways to fix this:

• The normal timeout rules could apply to unidentified invitees, or
• Participants could do their own timeout tracking of unidentified invitees, and uninvite any unidentified invitees that did not respond for too long.