Add toggle to hide/show images. #35

Initial:
![2014-07-30 at 10 54 am](https://cloud.githubusercontent.com/assets/4854/3751753/dce2d87c-1801-11e4-837e-e7abd4762959.png)

Hidden:
![2014-07-30 at 10 50 am](https://cloud.githubusercontent.com/assets/4854/3751743/bf909b6a-1801-11e4-8746-b583f7b1b234.png)