Users can sort auction by price and time

https://trello.com/c/LwsGn6iu/25-as-a-user-i-can-sort-auctions-by-time-left

https://trello.com/c/Cplgl2wU/24-as-a-user-i-can-sort-auctions-by-price

![image](https://cloud.githubusercontent.com/assets/8681076/5048991/b66f6218-6bef-11e4-82be-d1dc8930b6ea.png)

![image](https://cloud.githubusercontent.com/assets/8681076/5048996/bd13e828-6bef-11e4-9a89-35eb51c99807.png)

We don't actually need to make this an instance variable now, do we?