add a login dialog
To make Gajim more usable in places such as Internet cafés, it would be handy to have a login dialog like some proprietary IM clients have.
When enabled, such a dialog would show up at Gajim startup and prompt the user for their JID and password, optionally showing some last used JIDs in a combo box. Gajim would then create a temporary user account (which could be deleted at some point in the future, either manually or automatically), fill it with the entered JID, password and default settings, and open the roster with only this single account shown, not saving history.
This would be useful on machines which do not have separate user accounts, where standard Jabber account management would lead to accumulating users' JIDs in the application (unless each user deletes it after themself) and difficult login once the account setup wizard stops showing up (i.e. when there is another account set up).