Better errors

* Changes to support passthrough of errors from the API.  Previously we were providing misleading error codes in a lot of cases
* Added a test to make sure these passed through appropriately
* Moved the "load_tokens" call out of the initialize method.  In the pairing use case, this throws an error, since the client is not yet paired.  Refactored the "get_token" method to call load_tokens if the token is not found directly.
* Also corrected a minor error in the test formatting that was hardcoding a value instead of using the helper constant