VTK Viewport support for basic length measurements

[ohif-bot]

Created By: https://github.com/OHIF/Viewers/issues/743

Context:

We need a way to be able to measure distance between points in our 2D MPR views w/ VTK Viewports. VTK.js provides a basic example of how to accomplish this with it's Distance Widget:

• https://kitware.github.io/vtk-js/examples/DistanceWidget.html

Preferably, we would like to do this with their new SVG Widget Manager, but it may not yet be capable of this level of functionality.

Acceptance Criteria:

• [ ] New length tool added to toolbar
• [ ] Command to activate tool for all VTK Viewports
• [ ] Tool interaction is similar to the experience provided by cornerstone-tools length tool behavior
  • [ ] Visualization and text distance measurement (with correct units) appears on screen
• [ ] Measurement persists and updates correctly for scale/pan operations
• [ ] Measurement is cleared for rotation/reset and similar operations

[sedghi]

Cornerstone3D natively supports 3D and annotations, and is the main engine in OHIF right now.