Expose dispatch action type constants

Feature Request

Describe the suggestion or request in detail

In webchat customization scenarios, to set dispatch events or to intercept events using a middleware, the type has to be set to a string like WEB_CHAT/SET_TEXT. It would be great if you could expose the list of supported events as part of a constant so that we don’t have strings sprayed across the project and devs can check which events are supported. Also, If the text associated with a particular event is changed here for some reason, devs wouldn’t have to update it in their projects too.

[Enhancement]

[tdurnford]

It might also be nice to expose some of the action functions as well.

import { sendEvent, sendMessage, sendMessageBack } from 'botframework-webchat-core'

...

store.dispatch(sendMessage('Hello, World!')); 

However, we probably don’t want to expose some of the action functions such as the connection and speech related actions.

[cwhitten]

Loading this up for discussion and prioritization for an upcoming release.