fixed: Shutting down the Server could result in wrong presence state on
distant clients.

-> the in MobilisAgent.shutdown() a method sdm.removeFeature(...) was
called. Cause of introduction of Entity Caps, the capManager sends new
presence if features have changed. If the updated presence send by the
entity caps manager received clients after the unaivailable presence
send by the shutdown sequence, it could result in online presence state
on distant clients while node is offline.