Update TubeTK to work with VTK6

Change-Id: I3c22c1250a28c50f6184c2e0e634c1b9bb50ecb3
Merge branch 'WelcomeInterface-TubeTK'

* WelcomeInterface-TubeTK:
  Update TubeTK to work with VTK6

Change-Id: I3ae8038bb20e0ef22f8ead50b188a083822cf2dc