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
Can you wrap the contents of this template in two elements. The first element should be an article. Within that article, there should be a div with the wrapper class. It should be similar to the markup on the [about page](https://github.com/BaltimorePublicArtCommons/baltimore_public_art_commons/blob/master/app/views/static_pages/about.html.erb). It might not make the most sense, but at least the behavior is consistent.

We should refactor the the stylesheets and markup to make the intended behavior more clear, but we'll worry about that another day...