Replace ColorRamp with HSLColor everywhere.

Fixes:
* Nuclear-purple color exploit.
* #3247.
* Removes a bunch of unnecessary color conversions every frame.

Caveats:
* The ramp range is now defined on the palette, so ramps can no longer be set per-player (may impact maps which define custom colors).
* It's no longer possible to perfectly recreate the original WW color ramps (I doubt we care).
* The old ColorRamp setting isn't migrated, so players will lose their color settings.

OpenRA.Mods.RA/Widgets/Logic/DiplomacyLogic.cs

@@ -89,7 +89,7 @@ namespace OpenRA.Mods.RA.Widgets.Logic
 					Text = p.PlayerName,
 					Align = TextAlign.Left,
 					Font = "Bold",
-					Color = p.ColorRamp.GetColor(0),
+					Color = p.Color.RGB,
 				};
 
 				bg.AddChild(label);