Flag and city name change as event outcome

[Iceman 248]

Add flag_change and cityname_change as event outcomes.

The city names will be dynamic according to the civilization controlling the province, but sometimes the city name changes within the same civilization. An example of that is the current city of Volgograd that had three different names during the soviet era.

The same for flags. USA changed the flag multiple times to add more stars.

How it would work in the text files:

flag_change=civtag=newflagfilename (without .png)
Example: flag_change=usa=usa50

cityname_change=provinceID=newname
Example: cityname_change=123=Jakowski City