Populate the signed_in list with the names of currently
        signed in users.

def _set_signed_in(self):
        """Populate the signed_in list with the names of currently
        signed in users.
        """
        names = [
            controller.get_user_name(user, full_name=CONFIG['FULL_USER_NAMES'])
            for user in controller.signed_in_users()
        ]
        self.lbl_signedin_list.setText('\n'.join(sorted(names)))