Removed BYZ cores

Byzantium (BYZ) cores removed from those provinces that still had them.
Restored Antwerp provinces's trade bonus

Added the "centre of trade" modifier to Antwerp that had been mistakenly
removed.
Fixed no-religion for Icelandic vassal islands

Animism religion fixed to "animist" for Shetlands and Orkney provinces.
RIG to Merchant Republic

Riga (RIG) changed from theocracy to merchant republic as a better
representation of the proto-Hanseatic League.
Fixed eastern European country cultures

Many Eastern European countries had mistakenly capitalized
primary_culture values.
Added Formable Nations.

Added decisions to form the Formable Nation including some new nations.