Endocranial cavity segmentation tutorial

[muratmaga]

Based on the interesting thread Volume rendering produces block of "white noise" @Mark_1 has written an awesome tutorial on doing cavity segmentation in Slicer using three different approaches. Automated method described is now bundled with SlicerMorph, thanks to @lassoan.

https://slicermorph.github.io/Endocast_creation.html