Add a way to choose the preferred repository

**Is your feature request related to a problem? Please describe.**
When using _Droid-ify_, I always like to install the app _Breezy Weather_. When installing that app though, _Droid-ify_ always pulls the latest version with the higher number, ignoring the "FREENET" extension.

**Describe the solution you'd like**
Would it be possible to choose the preferred repository per app, as the regular _F-Droid_ client seems to do?

**Describe alternatives you've considered**
I've considered turning off some repositories, so the app can only be downloaded from the special "FREENET" repository that the _Breezy Weather_ developer offers. That would mean though that I'd have to turn off the _IzzyOnDroid_ repository and lose access to too many apps I also use.

**Additional context**
This is how apparently the official _F-Droid_ client solves this problem: