1. BeanstreamResponse:
changed fields to private final and added getters for sdk clients

added factory method that takes HttpResponse as input

added Builder to allow for appropriate default field values to be set without sacrifing final-ity,

and to support cases that necessitated incremental setting/storage of certain BeanstreamResponse values

2. Updated tests

3. Fixed bug in BeanstreamApiException (setting httpStatusCode field to "code" argument)