session: Remove potential infinite loop of logging out. When a user is logged in while the session is not available on the server side, and the user wants to log out, the logout request is started. When the server refuses to log the user out without a valid token and answers (correctly) with HTTP 401, the app calls the logout per default, which might end in an infinite loop. The logout procedure tests whether the users has a token stored. If so, the logout is called and the token is removed. In case the logout was answered with a HTTP 401 the cycle begins anew, but this time without token the user is treated as effective being logged out.

teichmann@intevation.de = sascha.teichmann@intevation.de
bernhard.reiter@intevation.de = bernhard@intevation.de