Issue 200 fix intersection

Fix for failing intersection issue #200 which generates an invalid Solid containing two disjoint parts when it should yield a single two part MultiSoild.

In summary, when recovering the vertices pertaining to each Polyhedra component of the desired intersection volume, we now process each 3-cell deemed relevant to the intersection result individually rather than collectively, since they may pertain to disjoint volumes. These volumes are now combined downstream as separate primitives, preserving the disjoint nature of the components of the result if they are indeed disjoint.

Also added a standalone test to demonstrate the fix.