Create combined inapp page (bug 1059944)

- Add new page which combines inapp keys and products
- Link out to docs
- Disable inapp products pages with waffle
- Add tests


![screenshot 2014-09-09 12 58 09](https://cloud.githubusercontent.com/assets/119884/4205631/89797798-3842-11e4-820a-9ea85a67b51c.png)
![screenshot 2014-09-09 12 58 18](https://cloud.githubusercontent.com/assets/119884/4205635/91b08b4a-3842-11e4-8c7d-58b46864e920.png)
![screenshot 2014-09-09 12 58 23](https://cloud.githubusercontent.com/assets/119884/4205641/9a8ab5e2-3842-11e4-8fa4-b33c5fb3c65d.png)

WIth in-app-products waffle disabled:
![screenshot 2014-09-09 13 02 44](https://cloud.githubusercontent.com/assets/119884/4205691/27c58fea-3843-11e4-824b-c0f53314cf34.png)


@cvan @mstriemer @andymckay @kumar303 


... "in the Firefox Marketplace Developer Hub." for consistency?