LevelBuilder support for play lab

[Finishes: #79639696, #79639780, #79639834, #79639722]
Hmmmm...I don't see any default code in the editor. Am I expected to?
![image](https://cloud.githubusercontent.com/assets/1767466/4512650/cc528aec-4b42-11e4-8d27-498bf5f7e850.png)