bug 1001704 - app for import/export of apps via SD card, r=fabrice

WIP patch

Basics in place:

* List installed apps, touch to export
* List apps detected in backup/apps on SD card, touch to import

TODO:

* Needs to hook up to the not-yet-landed import/export APIs
* Needs some styling improvements
* Tests
* Error handling
* Confirmation prompts?