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.FileFormats/OpenRA.FileFormats.csproj

@@ -77,7 +77,6 @@
     </Reference>
   </ItemGroup>
   <ItemGroup>
-    <Compile Include="ColorRamp.cs" />
     <Compile Include="Evaluator.cs" />
     <Compile Include="Exts.cs" />
     <Compile Include="FieldLoader.cs" />