Users

Covers the following stories: 
* users should exist
* Users should be able to marked as admins or catalogers
*Users should be able to login by going to /login
* Handle unsuccessful user login
* Add user information to secondary header after she has logged in
* Only logged in users can see the secondary header
'first_name' could just be first name. From a users perspective, the underscore isn't relevant. But I'm just being picky...