Add Endpoint for superusers to accept and decline new users without token

Currently the token is only delivered per mail. And without the mail link there is no way to accept or decline new users without accessing the backend. One solution might be to generate a new token when needed but there is no need for a token, when a superuser is logged in. That is why the easiest solution is to add a new endpoint for superusers to manage new users without token. (Until now the frontend didn't send a token with its request and an error would occur.)