Add support for SimpleSamlPHP, adding custom usernames and bulk creations of new users

Hi,

I have been using iF.SVNAdmin at a company where they have a AD with +100,000 users, so LDAP lookup is out of the question, this pull request adds SimpleSamlPHP integration so authentication can be done with ADFS or other SSO provides and also adds some code to add users without them existing in the htpassword file first. 

Regards Troels