[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.

### Screenshots
**Home page project preview**
![screen shot 2014-10-23 at 11 40 52 pm](https://cloud.githubusercontent.com/assets/153219/4752951/f278d6f8-5ab1-11e4-9636-dfdda45799f7.png)

**Reorder stages**
![screen shot 2014-11-10 at 2 16 33 pm](https://cloud.githubusercontent.com/assets/153219/4970772/e51fe196-6889-11e4-9ebb-8a528fafe7b9.png)

**Reorder stage commands**
![screen shot 2014-11-10 at 2 30 47 pm](https://cloud.githubusercontent.com/assets/153219/4970776/03860818-688a-11e4-9656-5c76b67147a3.png)