Change number of items to number of images for image viewer.

Closes #183 

#### Before
![before](https://cloud.githubusercontent.com/assets/96776/5017628/32913822-6a64-11e4-8db4-74c4cee46c1e.png)

#### After
![after](https://cloud.githubusercontent.com/assets/96776/5017627/32802fdc-6a64-11e4-9f8d-bd9b62943718.png)