use apps iframe for installs/launch (bug 1029687)

Use the iframe to:

- install apps
- query for installed apps
- launch apps

In market_button.html, check if the app is installed to render the right text rather than asynchronously updating the button after the app is rendered.
well, for one, if you install an app from Dev, that app will be marked as installed with an "Open" button on Prod and Stage. I'm almost certain @krupa will file for that.