[Repositories] Organize by categories

**Is your feature request related to a problem? Please describe.**
It becomes more and more painful with each update to look for a specific app repo in the list.

**Describe the solution you'd like**
An improvement could be to break repositories into sections:
- Official (F-Droid and F-Droid archives)
- Collection of apps (such as Izzy, Julian Fairfax's, etc)
- Apps [repos hosted by official maintainers of apps] (such as NewPipe, Collabora Office, etc)

**Describe alternatives you've considered**
#672 (IMO they are complementary and should both be implemented)