Added disconnect of sessions on shutdown [GATE-17], probe of sessions on startup [GATE-18], switched from XXXEnabled to XXX.enabled property [GATE-21], and added various listeners.

git-svn-id: http://svn.igniterealtime.org/svn/repos/wildfire/trunk/src/plugins/gateway@5102 b35dd754-fafc-0310-a699-88a17e54d16e