Add a tab to the credits panel for mod-specific text.

Enabled by adding a ModCredits block to mod.yaml.

OpenRA.Mods.Common/OpenRA.Mods.Common.csproj

@@ -882,6 +882,7 @@
     <Compile Include="UpdateRules\Rules\RenameEmitInfantryOnSell.cs" />
     <Compile Include="Traits\Render\WithBuildingRepairDecoration.cs" />
     <Compile Include="UpdateRules\Rules\SplitRepairDecoration.cs" />
+    <Compile Include="ModCredits.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <Target Name="AfterBuild">