- provide no_topology() characteristic to avoid triggering potentially
  expensive mesh connectivity calculations when they are not required.

- remove/deprecate unused pointField references from the renumber
  methods. These appear to have crept in from outer similarities
  with decompositionMethod, but have no meaning for renumbering.

- remove/deprecate various unused aggregation renumberings since these
  have been previously replaced by pre-calling calcCellCells, or
  using bandCompression directly.

- make regionFaceOrder for block-wise renumbering optional and
  treat as experimental (ie, default is now disabled).

  The original idea was to sort the intra-region and inter-region faces
  separately. However, this will mostly lead to non-upper triangular
  ordering between regions, which checkMesh and others don't really like.

ENH: add timing information for various renumberMesh stages

ENH: add reset of clockTime and cpuTime increment

- simplifies section-wise timings

ENH: add globalIndex::null() and fieldTypes::processorType conveniences

- provides more central management of these characteristics