[WIP] Feature/one on one presence

Add a Candy event for roster presence for people who are not in a MUC.

WIP
Hmn. I originally did plan for it because I wasn't sure if there was CSS available to handle the changes for each state, and for us at least we only currently use `available` and `unavailable` and figured at least this much is more than was implemented currently.

I'll have to look into it closer now that I'm looking at it again.