Integrate with entities from intent service

[sidecus]

NLP services like Luis supports entity extraction as part of the intent understanding.
It'll be better to connect PromptManager with those entities so that we don't have to ask user the info again.

It'll require IntentContext base class to have a new method which takes a parameter like a Dictionary and being able to automatically assign the entity value to corresponding user input properties.

Not too hard but didn't have time to implement it yet.