Gender law changes

Changing gender law now requires a certain level of prestige (500 for
Agnatic and Agnatic-Cognatic, 1000 for True Cognatic). The prestige is
not lost
Added Enatic-Cognatic and Enatic succession with some very high
restrictions. The AI will never use either
It is no longer possible to move directly from Agnatic to True Cognatic;
succession law has to be changed in steps: Agnatic -> Agnatic-Cognatic
-> True Cognatic -> Enatic-Cognatic -> Enatic