Users can delete their own listings

https://trello.com/c/Vn7cGtQO/42-delete-listings

![image](https://cloud.githubusercontent.com/assets/8669803/5095126/d484ad1a-6f34-11e4-90e1-f140dc85b03c.png)

![image](https://cloud.githubusercontent.com/assets/8669803/5095128/dc3f3a98-6f34-11e4-8830-072dbf2a3804.png)