feat: display status and idle time below contact name (if available)

XEP-0319: Last User Interaction in Presence along with the presence "status" message are both visible in gajim, but only in the roster view. Besides that, we have a "description" box below the contact name, that is only used for the description of a group chat. This MR uses this box in bare contacts to display "Idle since" and "Presence status".

I tested this MR with my XMPP account and it does not break anything.

I'd really like to have this in gajim, if this is not acceptable as a default behaviour, maybe I could make that an advanced setting?