checkMesh: Added writing of faceSets and cellSets containing errors

In parallel the sets are reconstructed. e.g.

mpirun -np 6 checkMesh -parallel -allGeometry -allTopology -writeSets vtk

will create a postProcessing/ folder with the vtk files of the
(reconstructed) faceSets and cellSets.

Also improved analysis of disconnected regions now also checks for point
connectivity with is useful for detecting if AMI regions have duplicate
points.

Patch contributed by Mattijs Janssens