Add identicon query param to GravatarPattern

This is part of #141 issue which turns teams/users without gravatar:

![d7efbb92-a091-11e3-8ee2-f8bba8488e35](https://f.cloud.github.com/assets/365089/2331889/039a04e8-a450-11e3-9a9a-3c1a4e91f23d.png)

to identicons:

![2014-03-05 16-19-32 project stub dashboard](https://f.cloud.github.com/assets/365089/2331893/117f269c-a450-11e3-903b-f125241d2663.png)