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" ?>
<datacage>
    <user>SA</user>
    <password/>
    <driver>org.h2.Driver</driver>
    <url>jdbc:h2:${artifacts.config.dir}/../h2/datacage</url>
</datacage>