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/Widgets/MapPreviewWidget.cs

@@ -130,7 +130,7 @@ namespace OpenRA.Widgets
 			TooltipSpawnIndex = -1;
 			if (ShowSpawnPoints)
 			{
-				var colors = SpawnClients().ToDictionary(c => c.Key, c => c.Value.ColorRamp.GetColor(0));
+				var colors = SpawnClients().ToDictionary(c => c.Key, c => c.Value.Color.RGB);
 
 				var spawnPoints = map.GetSpawnPoints().ToList();
 				foreach (var p in spawnPoints)