Feature/use absolute urls for client calls

Include unit tests for RequestContext class. Revert back to using absolute instead of relative imports within SDK. Inside of client base, expand truth checking of auth_token to include more than just None.  Use absolute urls instead of relative urls when making client put, get, post, and delete calls, which means that existing section methods and tests must form an absolute url based on request context and relative paths for methods.
Correct.  It's optional.  If you want to PUT or POST in JSON format, you'd need the matching content-type header and you'd also need to covert the payload to JSON.  We can consider providing an additional keyword parameter to all methods or all put/post methods that will lead to both of the above being performed for the request.