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 suppose it's not the perfect name. This was back when we didn't put Commonplace modules in their own folder and people were modifying helpers.js but not upstreaming so I made ```helpers_local``` (local to the project) and didn't think much about the name.