Add conversation ratings support

[thewheat]

Why?

Current code does not support reading conversation ratings of a conversation

How?

Add extra code to support reading conversation ratings

Open to feedback for the Customer and Teammate classes. They look the same currently so maybe best to make it a single class or inherit from one?

[apassant]

👍 I agree though that a parent class for Customer and Teammate would be nicer

[thewheat]

I've added a Participant class in #241 which is an addition to the Customer class. Before we merge this: I think we should think if having both Participant and Customer would be the best way to go because on the API end the input and output both refer to "customer"