Support for new QuickLook API

[relikd]

There you go. I tried to keep the changes to a minimum.

The new API requires to have an App target. Therefore, the "app" is the bare minimum "please open system settings".

And because it is an app, you'll need an app icon. I havent created one yet because I dont know what it should display. I can also help create an .icns file if you dont want to use Asset catalog.

Oh, and I have removed the developer certificate and sign locally. You need to re-enable that. :)

[relikd]

Oh, and you have to check whether it really works on 10.13. The compiler did not complain but I am still uncertain. (I know for a fact, that 10.14 is supported)