Add support for open contours

[cpinter]

Issue reported in http://www.na-mic.org/Bug/view.php?id=4087 Adding this support will be also useful for future projects.

The open contours are to be loaded to segmentation objects with

• Non-planar contour
  • Contains the raw contour points
  • Converter is needed to closed surface
• Closed surface containing the tube model
  • What should be the radius of the tube? Half of the slice thickness calculated from the planar contours from the other contained structures? Constant 1mm? -> Start with 1mm, it will be a conversion parameter

Migrated from https://app.assembla.com/spaces/slicerrt/tickets/786-add-support-for-open-contours/details