Add Slack real time API functionality to client

[dalanmiller]

To my knowledge, most of the OAuth Provider APIs are pretty request/response based but having familiarity with the Slack API, it would be great to allow for some sort of functionality to allow Slack authenticated users to access the Slack real time messaging API.

Basically we just need to expose a function in the currentUser API which uses their token to make the initial request. This returns JSON and a 30 second TTL'd WebSocket URL which can be started in the browser with a function handler passed to handle the incoming streaming events.

This would allow for really neat Slack meta-applications to be built, such as question monitoring, pseudo-bots, presence dashboards and much much more! ✨

[deontologician]

This would be a really good module. We could get an idea of how third party modules should be implemented.