Add ScriptCS C# Responder

Here's a ScriptCS C# responder (I haven't tested it in this pull request, but it works with my Docker setup).

If you are new to ScriptCS on Mono, you can do this (assuming mono is installed):

1. `git clone https://github.com/scriptcs/scriptcs.git && cd scriptcs/ && ./build.sh`
2. `cd src/ScriptCs/bin/Release/`
3. `mono scriptcs.exe /path/to/responder.csx`

Note: On step 3, it should auto-install the nuget packages and then run, but if it doesn't, you can do `mono scriptcs.exe -install RabbitMQ.Client` and place the `packages/` directory in the `responders/charp/` path. I think you can probably make a bash script to do the `mono scriptcs.exe` stuff and place it in `.foreman` / `Procfile`. Please let me know if you have any questions.