Mod setting option for custom color

[Caedendi]

This issue is a direct result of the discussion here.

It would be nice if the D2RMM mod settings (mod.json) could get a new setting type for custom color values.

Color variables in _profilehd.json and related consist of 4 number values: red, green, blue and alpha. At the moment this would require 4 large and unintuitive separate number setting fields for each custom color you'd like to make available for your mod, and it would be unreadable and error-prone if you need a lot more like in the link above.