Merge branch haouech:cwlparser (#38) into cwlparser

Contributed by Majdi Haouech @haouech
(ASF ICLA on file)

Add structural import for a CWL workflow to Apache Taverna.  The current
code parses the cwl file to extract inputs, outputs and steps of a
workflow, and then converts them to a Taverna workflow containing ports,
processors and data links.

This closes #38