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.
I'm not asking you to fix the spacing everywhere, but I'm not sure why you would add unnecessary spacing for no reason. every byte counts.