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.Game/GameRules/Settings.cs

@@ -110,7 +110,7 @@ namespace OpenRA.GameRules
 	public class PlayerSettings
 	{
 		public string Name = "Newbie";
-		public ColorRamp ColorRamp = new ColorRamp(75, 255, 180, 25);
+		public HSLColor Color = new HSLColor(75, 255, 180);
 		public string LastServer = "localhost:1234";
 	}