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.Editor/Surface.cs

@@ -357,7 +357,7 @@ namespace OpenRA.Editor
 		{
 			var pr = Map.Players[name];
 			var pcpi = Rules.Info["player"].Traits.Get<PlayerColorPaletteInfo>();
-			var remap = new PlayerColorRemap(pcpi.RemapIndex, pr.ColorRamp);
+			var remap = new PlayerColorRemap(pcpi.RemapIndex, pr.Color, pcpi.Ramp);
 			return new Palette(PlayerPalette, remap).AsSystemPalette();
 		}