Created FlashPaletteEffectWarhead and removed the hardcoded flashing from NukeLaunch

Not actually hardcoded, but there was a hard dependency in NukeLaunch on FlashPaletteEffect and explicit flashing checks.

OpenRA.Mods.Common/UpdateRules/UpdatePath.cs

@@ -67,6 +67,7 @@ namespace OpenRA.Mods.Common.UpdateRules
 				new ConvertSupportPowerRangesToFootprint(),
 				new UpdateTilesetColors(),
 				new UpdateMapInits(),
+				new CreateFlashPaletteEffectWarhead(),
 			})
 		};