[WIP][POC] Add support for nested stages

Proof-of-concept to allow stages to be nested, allowing for meta-stages or groups of stages to deploy to multiple environments at once.

![screen shot 2014-10-23 at 11 40 52 pm](https://cloud.githubusercontent.com/assets/153219/4752951/f278d6f8-5ab1-11e4-9636-dfdda45799f7.png)