Add an abstraction layer over the Slack client to make changes easier in the future

[bbaga]

Is your feature request related to a problem? Please describe.
Recently had to migrate from HubSpot's client to the official slack client, it could have been a lot less work if there was an abstraction layer.

Describe the solution you'd like
Create an abstraction to cover the slack functions currently used, so we can hide the actual client's implementation details.

Describe alternatives you've considered
Chances are, there won't be many changes in the future, but still, better to this sooner than later.