ENH: consolidate processorTopology handling for volume and area meshes

- relocate templating to factory method 'New'.
  Adds provisions for more general re-use.

- expose processor topology in globalMesh as topology()

- wrap proc->patch lookup as processorTopology::procPatchLookup method
  (failsafe). May consider using Map<label> for its storage in the
  future.

applications/utilities/mesh/generation/extrude/extrudeMesh/extrudeMesh.C

@@ -60,6 +60,7 @@ Description
 #include "wedgePolyPatch.H"
 #include "planeExtrusion.H"
 #include "emptyPolyPatch.H"
+#include "processorPolyPatch.H"
 #include "processorMeshes.H"
 #include "hexRef8Data.H"