Adds thumnail on catalog page.

 Closes #32. @kevinreiss, I think we should go for having the thumbnail or 
 the link ("View Images (_n_)") above launch the modal. Looks like this right now:
![screenshot from 2014-12-16 17 08 06](https://cloud.githubusercontent.com/assets/999701/5463005/183cd8ca-8547-11e4-8b6d-21088b233c65.png)