Adding "role" model translation

Adding "role" model translation.

_Screenshots:_

Without translation:

![screenshot - 07212013 - 09 37 31 pm](https://f.cloud.github.com/assets/1538066/832617/ec46a026-f266-11e2-94a7-fe957deb3932.png)

With translation:
![screenshot - 07212013 - 09 39 01 pm](https://f.cloud.github.com/assets/1538066/832619/1f3da1b4-f267-11e2-92a7-6ef6b5722814.png)