[JM-1235] Added ability to kick users from admin console.  In the future it would be nice to be able to kick owner/moderators as well, but that'll be part of the great ACL improvements.

Also fixed a potential NPE that could occur in TabsTag.

git-svn-id: http://svn.igniterealtime.org/svn/repos/openfire/trunk@9811 b35dd754-fafc-0310-a699-88a17e54d16e