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.
for the `paid` class, we do that logic in [`market_tile.html`](https://github.com/mozilla/fireplace/blob/master/hearth/templates/_macros/market_tile.html#L65) and pass it in `classes`. we should probably do the `classes` in the same place. so either, move that line here or move the `installed` there.