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 just followed some silly personal pattern that I reference function in variables if they will be exported by the module. And name the function if it is an internal function.