Add support for NET Standard support via new Microsoft.Azure.ServiceBus client

[niemyjski]

Thanks to @shahbarkha for her awesome work on the client! Please use the nightly builds from myget & nuget.. These builds should be considered stable but we have decided against pushing them live until a future date. Our reason for doing so is we are not happy with Microsoft's new Management libraries which require you to put Azure AD credentials into your app to use the service bus. They have heard the community loud and clear and are working towards a rewrite (v2) of the management API that uses connection string management like the legacy client.

[CLAassistant]

All committers have signed the CLA.

[niemyjski]

@shahbarkha I think we just need to resolve all conflicts and use your version completely ignoring master

[niemyjski]

I'm leaving this open as this fixed several tests as well as logging improvements that we need to bring into master.