ENH: relocate/refactor fvMeshSubset

- direct construct and reset method for creating a zero-sized (dummy)
  subMesh. Has no exposed faces and no parallel synchronization
  required.

- core mapping (interpolate) functionality with direct handling
  of subsetting in fvMeshSubset (src/finiteVolume).
  Does not use dynamicMesh topology changes

- two-step subsetting as fvMeshSubsetter (src/dynamicMesh).
  Does use dynamicMesh topology changes.
  This is apparently only needed by the subsetMesh application itself.

DEFEATURE: remove deprecated setLargeCellSubset() method

- was deprecated JUL-2018, now removed (see issue #951)

applications/utilities/parallelProcessing/redistributePar/redistributePar.C

@@ -1031,10 +1031,7 @@ autoPtr<mapDistributePolyMesh> redistributeAndWrite
 
             // Subset 0 cells, no parallel comms.
             // This is used to create zero-sized fields.
-            subsetterPtr.reset
-            (
-                new fvMeshSubset(mesh, bitSet(), nonProcI, false)
-            );
+            subsetterPtr.reset(new fvMeshSubset(mesh, zero{}));
         }