refactor wsgi authentication script

[Reimar Bauer]

In a context where we do use different users than www-data we should care that the wsgi authenticator script also runs on that different user.

see also #118

[Reimar Bauer]

the simplest solution is to split the configuration into one for mss_settings and one for mss_auth

the auth.wsgi must not have access to anything else than allowed_users

[Reimar Bauer]

refactored wsgi auth handler, fixes #141, #118

→ <<cset d07b7136dd18>>

[Reimar Bauer]

Merged in ReimarBauer/mss (pull request #228)

refactored wsgi auth handler, fixes #141, #118

→ <<cset b0c26af893e5>>