Users can sort auctions by name

https://trello.com/c/c1sAlUTC/35-as-a-user-i-can-sort-auctions-by-name

![image](https://cloud.githubusercontent.com/assets/8681076/5014407/799b83e0-6a63-11e4-881a-2d3e7f9ebf43.png)

![image](https://cloud.githubusercontent.com/assets/8681076/5014411/7f35e516-6a63-11e4-80e3-1f948795352e.png)


Use `image-url` instead of `url` so that your app doesn't break in production.

When assets are compiled for production, `up_arrow.gif` becomes e.g. `up-arrow-1ae34fa.gif`, and this will break. `image-url` is a special SCSS helper that will refer to the file no matter what its name is.