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
@latazzajones sorry I missed this, but the markup isn't quite right. The `if` statement should be around the entire span, because the span should only be rendered if a user has logged in. There is also a closing `</section>` tag without an opening tag. The closing `</section>` tag probably doesn't need to be here. Finally, the span has a `login-status` class that isn't defined in the stylesheet. Please remove it if it isn't needed.

Please change the markup and submit a new pull request.