Add colors to regions

[Idhrendur]

Use them to define map and flag colors for unrecognized nations.

Maybe also use them to tweak the color of dominions from the parent country colors.

[IohannesIohannium]

Added them in the configurable through #1414.
They should be added in code. While "unrecognized" nations would simply get the region's true color, generated dominions should have the colour calculated by two parts overlord, one part region. That is, if the overlord is { A B C } and the region { X Y Z }, the generated dominion's color should be { [(2A+X)/3] [(2B+Y)/3] [(2C+Z)/3] }, rounded to integers.

[Idhrendur]

The particulars of the generated dominion colors I'd tweak. They should be modified from within the HSV color space so they're recognizably similar to the overlord color.