Introduce AppFeatures to the app submission/update flows.

## Submission

![submission](https://f.cloud.github.com/assets/23885/473757/e492b7a2-b756-11e2-97fc-d6b456f16169.png)

## Update

![update_display](https://f.cloud.github.com/assets/23885/473772/39579032-b757-11e2-83ab-c8c61f8fbd32.png)
![update_edit](https://f.cloud.github.com/assets/23885/473773/397a63be-b757-11e2-8c00-1cfd5683d3b5.png)