Add smoothing factor in GUI to drive the vasculature analysis

[RafaelPalomar]

There are some reported cases where low quality meshes generated by segmentations may prevent the centerline extraction from happening.

https://discourse.slicer.org/t/extract-centerline-fails-when-calculating-the-centerline-with-tree-window/25546

It seems that changing (or enabling) the mesh smoothing solves this problem. Adding a slicer/spin-box to change the smoothing factor of the underlying mesh participating in the centerline extraction would help the users to overcome this problem.