add new modules
Add dedicated module for authentication.

Refactored parts of login and idp_user into this new module.

Also got rid of some cherrypy leakage into login.py.
Log tinkering.
Don't pass SSO session id in URL parameter.

There is no need to pass the SSO session_id in an URL parameter when
it is also sent to the users browser as a cookie.

In fact, it is preferable to NOT have it in the URL since these URLs
are bound to be put in an e-mail (perhaps to support) sooner or later.
Update the login flow documentation.
Remove artifact endpoint.

Talked to Roland - SAML artifacts aren't used in the SWAMID
federation, and it is time to purge any unused (and therefor
untested) code from this IdP.