Fixing XSD conflict on imports with same namespace

When a WSDL imports more than one XSD file with the same namespace, the last imported XSD is overwriting the definitions brought by first ones. The solution I found is to deep-merge (using a lodash function) the definitions instead of overwriting it.

To ensure nothing else was broken by this change, I created a test case (see test/wsdl/include_with_duplicated_namespace.wsdl file).

Hope this pull request get merged =)