#2 Authentication

Implements #2, allowing for both CAS and email/password authentication. Refer to the issue for commentary; this PR includes significant changes including guest user functionality, integration tests, and more!

Issues Resolved (please check all during review):
* #2
* #694 
* #777 
* #965 
* #973
* #1018
Since we were using a gem from a specified git repo (and not the standard rubygems library) I believe that `Gemfile.lock` includes the remote information. Once we took that gem out the whole section was removed.