#41 "exit handler" and idle flush

[Benny Lofgren]

It would be helpful if OpenKOM caught SIGTERM and
SIGHUP (or its java equivalents) and performed a quick
user cleanup to save user status, conference pointers
and so on.

In fact, it might be a good idea to periodically flush
idle users' status (if dirty), to minimize the impact
of a sudden system crash.