when new roster entries are added, make sure they are on the local list
improve groupchat user interface/setup
don't update remote sessions; if jabberid changes, create new session
make sure to not throw a NPE if last cursor is null
the user can't do anything about these error messages so let's not make it worse
TODO improve error message handling automatically
SessionID instances must NOT be held anywhere, as they change
a new SessionID can be created if the remote user /resource changes
Merge pull request #551 from n8fr8/master

3 fixes