Reintroduce a grey border to the workspace thumbnails, so they don't shift when selected
Merge pull request #128 from fvichot/workspace-switcher-qss-border-fix

Reintroduce a grey border to the workspace thumbnails
First try at switching to vtkImageView for thumbnails generation
Correct bug in vtkImageView
Add itkThumbnailGenerator, works for 3D and 4D scalar images
Cleaner thumbnail generator, propagate mirror to vtk meshes
Remove duplicated method
Remove warning in plugin generator
Negate if conditions and avoid leakage