Unrestricted Unification alternative rule

[moretrim]

It should be possible to replace every check of the form:

NOT = { has_country_flag = post_colonial_country }

into a form that also looks for a game rule. This would enable the players to select an alternative rule where colonial countries are no longer excluded from unification decisions/events and similar.

It remains to be seen if that can or should be extended to other decisions/events.