Extended the AuthenticationCallBackProvider so we can manually filter domainnames.

We use the google apps, and would like to use Jabbr as our chatclient.
We only want to have users in the chat with our domainname (sso via
google). This implementation implements that request
Merge pull request #2 from micheltol/JabbRAuthenticationCallbackProviderExtension

Extended the AuthenticationCallBackProvider so we can manually filter do...