Merge topic 'vtkweb-python3-support'

* vtkweb-python3-support:
  Web: Python 3 support - Python 2 module merged
  Web: Python3 compatible changes, future imports
  AutobahnPython: python3 compatible changes backport
  Twisted: clean up update.sh, remove Contributing
  Twisted 2017-03-30 (83a3a529)
  ThirdParty/Twisted, add update.sh script, readme
  ThirdParty Twisted: remove old version, import prep

Merge-request: !2649