Implement UserService method to remove current user from session For being able to logout a user UserService must provide a method the remove the current user object from the session. Part of flys/issue916 (Logout: "Abmelden" Knopf mit Funktion belegen)

<?xml version="1.0" encoding="UTF-8" ?>
<rest-server>
    <!--  The port which the ArtifactDatabase (ArtifactServer) will bind to. -->
    <port>8999</port>
    <listen>localhost</listen>
</rest-server>