S3_1 version adds optional network capability.
This fixes the most important case of knowing if your own city fulfills "CityStatus" "OwnedByOriginal" or "OriginalOwner" requirements. Unowned (potentially fogged, even destroyed in reality) cities we cannot support without savegame format changes -> 3.2: #46468
Blocked by #46503, on the basis that this exposes the issue of that ticket significantly more seriously. Some changes to this ticket too required once it gets fixed.
Rebased on top of #46503, some changes related to it (mainly comments, now that we KNOW that 'original' is sometimes NULL also on the server side)
Testing "CityStatus" "OwnedByOriginal" requirement (on master). The client seems to think that a city the player conquered is under original owner - server does not accept.