Add croppable avatar for exhibit contacts

![screen shot 2014-11-26 at 4 07 11 pm](https://cloud.githubusercontent.com/assets/111218/5210697/6c3ac976-7586-11e4-8e31-91eed46b1f1b.png)
![screen shot 2014-11-26 at 4 08 01 pm](https://cloud.githubusercontent.com/assets/111218/5210698/6c4f9fc2-7586-11e4-83df-086eacbcf2af.png)
![screen shot 2014-11-26 at 4 07 18 pm](https://cloud.githubusercontent.com/assets/111218/5210699/6c58cd5e-7586-11e4-9a68-0d2dbdc05a94.png)