Let the F-Droid descriptions be localized

This moves the summary and description for the F-Droid apps to the metadata/ folder, where it can be fully localized by our translators working on Weblate.

The same idea as !2262 (merged)

rebased on the latest master. @mimi89999 this is ready to merge IMHO

I replaced "Application manager" with "The app store that respects freedom and privacy", otherwise the texts are unchanged. None of that is set in stone, once we figure out good language in fdroid-website!17, I'll update the description files here. "Application Manager" seems like it would be basically meaningless to most mobile users, especially those who do not already know F-Droid.

merged

mentioned in merge request !2342 (closed)

mentioned in issue fdroidclient#1100