support for CompositeTemplates

As documented in https://www.docusign.com/p/RESTAPIGuide/RESTAPIGuide.htm#REST%20API%20References/Send%20an%20Envelope%20from%20a%20Template.htm

Needed in order to send a template with pre-populated values.
No sysouts allowed in commit. For a case like this, write a reusable method in Utility class to return pretty string from dto and call it here. Replace sysout with logger.debug and printStackTrace with logger.error