link from devhub to commbadge (bug 907569)

Previous attempt: https://github.com/mozilla/zamboni/pull/1088

If no comm thread, link to ```/comm/```

If comm thread, link to ```/comm/thread/<thread_id>```

**Screenshots**
![screen shot 2013-09-30 at 2 50 14 pm](https://f.cloud.github.com/assets/674727/1241280/54fecbda-2a1a-11e3-8ab7-45cf5ff0bff0.png)
![screen shot 2013-09-30 at 2 50 19 pm](https://f.cloud.github.com/assets/674727/1241281/575520f0-2a1a-11e3-8afd-50adad6cccfd.png)

![](http://i.imgur.com/Kh2Osoy.gif)