ENH: faMeshReconstructor for reconstructing equivalent serial faMesh (#2084)

- A bare-bones reconstructor for finiteArea meshes when processor
  meshes are available (in parallel) but an equivalent serial faMesh
  is needed for reconstruction or decomposition.
  In these situations, a serial version of the faMesh is needed,
  but preferably without reconstructing the entire volume mesh.

  It uses the finiteVolume faceProcAddressing in addition to
  the geometric information available from the underlying polyMesh.

  The resulting equivalent faMesh can be used for basic operations,
  but caution should be exercised before attempting large operations.