App modules: add additional properties for benefit of testing, add-ons and alike #7894

Hi,

Sprang from a discussion on Gitter:

A new add-on developer asks if a property to return the full path for an app be created. @jcsteh gave a solution. And since I've been meaning to add a few more properties (namely detecting if we're dealing with a universal app or not), I though it would be best to raise a meta-issue here.

Thus please let us know if you need properties about an app that should be shown as part of an app module.

Thanks.