Allow for the outline color to be changeable

[vabold]

The current behavior is to invert the current on screen text color. If the color is set to 0xFF00FFFF, the outline color is 0xFFFF0000. This means the outline is red and the text is blue, which looks horrible.

[ximk]

I think just having the option between a black or white outline would be enough here to solve the issue while still keeping the interface simple.