DRY on clients

[Gonmeso]

There is a lot of code duplication in the clients mainly because each action handles the request by its own. A couple of ways to improve and follow the DRY principle would be:

• Create a perform_request/handle_request functionality at base ApiClient so it handles the headers (now done in each function) and the requests params. Kind of how requests does it, as it has a main request function and the underlying GET, POST... methods call it under the hood. Check it.

• Create base get, list and create methods in ApiClient as many of the resources use the same way to retrieve information, for example a get basically needs an object id to retrieve the information.