Use qrc instead of assets when making Qt Quick 2 Application on Android

The "Qt Quick 2 Application" wizard will currently use assets as the way to bundle files on Android. This is not the recommended "best practices" since querying and loading assets is known to be quite slow.

One user reports reducing his app's start-up time from 12 seconds to 3 seconds when moving all the files into a qrc file instead.

Using qrc has the added benefit of being a cross-platform solution, so that we won't need all the platform-specific code in the template.