more prompts

[billba]

Need implementations for the following types of prompts (roughly in order of importance):

• choice
• confirm
• datetime
• attachment
• OAuth

botbuilder-dialogs is a good place to start.

[Stevenic]

You might add the new OAuthPrompt to this list as its both useful and will definitely be a good test of your overall prompt architecture.

[billba]

I would welcome a pull request :-)