Initial stab at shibboleth authentication

This is an initial implementation for https://github.com/bergie/passport-saml/issues/10

I've added some documentation in the README file explaining what's required to set up the app. Once you've set up the app (with the metadata route), you should retrieve the metadata, save it in some `uniquely-named-xml-file.xml` and register your app as a SP with testshib.org

I found it easiest to add a host in my /etc/hosts and proxy node via nginx and added https (as I think Shibboleth refuses to work over anything else than https)

It should then be a matter of browsing to your initiator route and get redirected to the testshib IdP.

I've pushed the Java code to https://github.com/sakaiproject/SAMLParser (check the readme for compiling it)

I realize it's a bit of a hassle to set it all up, so feel free to contact me via mail at gaeremyncks@gmail.com or `simong` on Freenode if anything isn't superclear.