modding: Ignore ruleset-specific errors when unique is disabled in this ruleset

By SomeTroglodyte:
- Hide religion- or espionage-specific demands when disabled 
- Fixed NPE when Espionage Screen is used to move a spy to an unknown civ's city 

By unciv-loof:
- Add missing table row for city resistance 

By Ambeco:
- Unciv can receive links directly to games or new friends
- Prevent save-scumming for more types of randomness

Added option to stop workers from removing vegetation - By Emandac