@dzucconi: "Fillwidth" row layout for artworks

This adds an alternative layout where artworks are laid out in a row that fills it's container's width. I opted to not use [my fillwidth](https://github.com/craigspaeth/jquery.fillwidth) plugin because this only deals with one row and doesn't have to accommodate as many edge cases as jquery.fillwidth does. The logic was much simpler and so it was actually easier to rewrite this small bit than try to shove jquery.fillwidth inside the component.

![cap](https://cloud.githubusercontent.com/assets/555859/4890633/be78f214-63a0-11e4-817b-9b89850dc082.gif)