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/World/DebugOverlay.cs

@@ -57,7 +57,7 @@ namespace OpenRA.Mods.RA
 
 			foreach (var pair in layers)
 			{
-				Color c = (pair.Key != null) ? pair.Key.ColorRamp.GetColor(0f) : Color.PaleTurquoise;
+				Color c = (pair.Key != null) ? pair.Key.Color.RGB : Color.PaleTurquoise;
 				var layer = pair.Value;
 
 				for (int j = mapBounds.Top; j <= mapBounds.Bottom; ++j)