Initial CSS additions for Shelf Nav Item

Hey everyone (Dave / Connor / Jacob?)!

This is the first half of getting the shelf navigation item working. See a recorded demo here:

https://vimeo.com/53781844

Or this rather ugly screencap below:

<img src="http://i.imgur.com/A4RuD.png"/>

The high level idea behind how the shelf will work:

* The shelf navigation element always exists, it just has a CSS attribute to hide it normally
* A shelf nav item that receives the  css class ```exposed``` will translate into view
* Adding the css class ```shelf_exposed``` to the body element will translate bar-titles, bar-tabs, and the div.content to the side. Essentially this class on body acts as a global "a shelf is shown" variable.
* Since each shelf is exposed individually but the entire viewport is translated globally, you can have multiple shelves

After this, I'll just need to add the JS that triggers these classes for a given link.