Mesh_3::Add handling of *.nii files in one example

[afabri]

Summary of Changes

While the Polyhedron demo can read *.nii files there is no example in examples/Mesh_3/.
This PR adds the functionality to the example that uses vtk to read DICOM data.

This is triggered by this question on stackoverflow.

• Support of *.nrrd format
• example for segmented images
• Add example data for the file formats.

Release Management

• Affected package(s): Mesh_3
• License and copyright ownership: unchanged

[sloriot]

Successfully tested in CGAL-6.0-Ic-96

[lrineau]

@afabri This PR still have several TODO items. Should I wait or merge it?

[afabri]

@afabri This PR still have several TODO items. Should I wait or merge it?

Wait.

[sloriot]

@afabri, this PR was marked tested 3 month ago and is still waiting for some TODOs. Maybe you want to open an issue instead and integrate the PR.

[github-actions]

This pull-request was previously marked with the label Tested, but has been modified with new commits. That label has been removed.

[sloriot]

Successfully tested in 6.0-Ic-251