Pivoting a TraversalURIOptimisedQuery is broken in release 1.13.2

Pivoting a TraversalURIOptimisedQuery is broken in release 1.13.2

- fix query building for TraversalURIOptimizedQuery
- enable DataLinkTests for TRAVERSAL_URI again
- add further tests to test pivoting more directly
- roll back version to 1.13.2 to rerelease fixed version
- add python six dependency to fix upstream issue with sphinxcontrib-swagger dependency

Issue-ID: AAI-3758
Signed-off-by: Fiete Ostkamp <Fiete.Ostkamp@telekom.de>
Change-Id: I3e54216e00d0491d64265e149f55cf8aba6fabd9