Fixes to player vassals in civil wars

Adds new game rules to customize MIV.

Adjusts custom AI empires/kingdoms frequency.

Fixes normal Great Wars not triggering

Great Wars mechanic no longer affects starting event wars (Hungarian migration, norman/norwegian invasion of england, sons of lothbrok, etc)

Fixes a small issue

Tribes and clans are now noticeably more aggressive and expansionist, while feudals wage fewer wars but are more stable and often have larger sub realms that can help protect the realm

Strengthen AI realms

Small fixes

AI war declaration logic is now smarter