Make southern Africa (Boer, Matabele, Zulu) flavor more immersive

[rogerburks]

Another placeholder issue that I will expand later. Currently, the game causes Boer expansion to instantly displace whoever is occupying Transvaal and Oranje provinces. While this should likely be the end result in nearly all cases, it could happen in a more elegant and immersive way that would make the player feel more involved when playing relevant tags.

Especially:

• Matabele, or whoever owns involved provinces, should have the opportunity to resist or control Boer expansion, even if it is very challenging. This is more immersive than an instant event.