Update wiki page for Shibboleth and CAS authentication

The authoritative wiki document for enabling Shibboleth authentication for Grouper is a contribution page from Newcastle University which was last updated 2012. It is mainly for getting the admin UI to work, so a lot of the information is no longer relevant. The page also uses "shib" instead of shibboleth almost exclusively, and never uses terms SSO or single sign-on. This makes the page hard to find, even though it's the page everyone needs to find if they want to set up Shibboleth.

The instruction page for CAS is a Cal Poly contribution page. Rightly or wrongly, this page has been maintained since 2012 by the Grouper team and not Cal Poly. Should the page be moved to a more central location if we're maintaining it?