Add image carousel

https://trello.com/c/ddWJgvwi/31-improve-image-gallery-displays

![usercarousel](https://cloud.githubusercontent.com/assets/8681076/5284363/ae0a9786-7ae1-11e4-9158-a0458270331d.gif)

![sitecarousel](https://cloud.githubusercontent.com/assets/8681076/5284347/88f9fc2a-7ae1-11e4-8fc2-d9c7df91a727.gif)