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/Effects/Contrail.cs

@@ -61,7 +61,7 @@ namespace OpenRA.Mods.RA
 
 		public static Color ChooseColor(Actor self)
 		{
-			var ownerColor = Color.FromArgb(255, self.Owner.ColorRamp.GetColor(0));
+			var ownerColor = Color.FromArgb(255, self.Owner.Color.RGB);
 			return Exts.ColorLerp(0.5f, ownerColor, Color.White);
 		}