Users can add pictures to dive sites

https://trello.com/c/LuI1FslQ/19-add-images-to-dive-sites

![image](https://cloud.githubusercontent.com/assets/8681076/5078654/674d3964-6e7c-11e4-8a9c-3812afb8f2e1.png)

Does an image belong_to a dive site?