Phoenix

Based on the answer of @olivermue I added some stuff for the response handling. 1st I added the classes for mocking the request and the response. ```c# public class GraphBatchRequestMock...

Maybe you have to switch the `message.Content.Headers.ContentType` in the Mock of `ConvertToNaiveRequestAsync` to a more suitable for streams (e.g. `application/octet-stream`), but this is just a guess, i didn't test this...