Afro-colonial culture generation

[IohannesIohannium]

Same mechanisms as of #74, but with forced African ethnicities

[Zemurin]

This issue is related to a general overhaul and implementation of african/slave culture injection system into pops of the new world. Currently we don't have any afro-* cultures in the new world unless the african nations colonize it.

I would very much like to generate appropriate afro-* cultures and settle them in the New World, as slaves or free (depending on country laws).