nested tabs for builds

![canary](https://f.cloud.github.com/assets/1131196/1080020/8c692ee8-1558-11e3-83fe-4685a09e0e28.png)
![release](https://f.cloud.github.com/assets/1131196/1080022/8f3fbcea-1558-11e3-8be2-6b1cca448acc.png)