Split up chrysom client

[kristinapathak]

We can split up the current chrysom client in order to separate the two main use cases of the current client: direct requests and polling. This will allow the code to be more modular, and I think it will aid in maintainability long term.

I'm proposing to have a BasicClient that provides the wrapper for http requests to argus, and then use that in a ListenerClient that uses a long running goroutine to poll argus for items.