Add custom mesh correction for the mesh produced by Iso2mesh

[fussegli]

Detect tetrahedrons that belong to same phase and are in contact through only one edge or one vertice, then remove them (i.e., assign them to the adjacent phase).
That's the same approach I am already using during the pre-processing, but applied on the mesh and not on the 3D array (see the morphology opening section of the meshing module documentation).