Using non-default packages in BridgeMessenger

I need some packages in my `BridgeMessenger`, but I can't use the `using` directive in the code, because these directives are inserted at a place where `using` is illegal during Launcher compilation (see https://docs.microsoft.com/en-us/dotnet/csharp/misc/cs1529 ).

How can I use packages like `System.Net.Http` or `Newtonsoft.Json` in my `BridgeMessenger`?

*Edit:* Another problem that came up is that even when I edit Grunt templates to include the appropriate `using` directives, the compiler doesn't seem to find the requires assemblies, although they are added to the Covenant project.