First commit of a bunch of user related stuff in a separate branch.

* Create User model that authenticates with CAS and then populates the
  user information using the Hesburgh Person API.
* Added validation that user exists in in the Hesburgh API.
* Write some rspec tests.

dec-20#
Merge pull request #1 from ndlib/user-related

First commit of a bunch of user related stuff in a separate branch.