For Teams we need sample of how to hand Invoke activity to Dialog

[johnataylor]

In the case of Teams the OAuth Prompt needs to see the Invoke activity. By default the ActivityHandler doesn't give this to the Dialog, instead this is left as a job of the application (the assumption being the application would subclass and specialize the ActivityHandler.)

[johnataylor]

Refer to microsoft/botbuilder-dotnet#1979

[johnataylor]

Both C# and JavaScript checked in. These are basically Teams specific versions of the auth sample (18).