- add placeholder BoundaryMesh to surfMesh allows us to drop the
  SurfGeoMesh class and just reuse the GeoMesh class.
  Do the same for triSurface.

- renamed surface regions (formerly patches or groups) to surfZone.

- added surfMesh, but without any of the patch information needed to make it
  useful for finiteArea.

- promoted coordinateSystem transformation to surfaceMeshConvert and moved
  old to surfaceMeshConvertTesting.

- moving back to original flat addressing in iterators means there is no
  performance issue with using lazy evaluation
- set() method now has ~0 for a default value.
  We can thus simply write 'set(i) to trun on all of the bits.
  This means we can use it just like labelHashSet::set(i)
- added flip() method for inverting bits. I don't know where we might need
  it, but the STL has it so we might as well too.

- dropped auto-vivification for now (performance issue), but reworked to
  allow easy reinstatement
- derived both iterator and const_iterator from iteratorBase and use
  iteratorBase as our proxy for non-const access to the list elements.
  This allows properly chaining assignments:
     list[1] = list[2];
     list[1] = list[2] = 10;
- assigning iterators from iteratorBase or other iterators works:
     iterator iter = list[20];
- made template parameter nBits=1 the default

    - convertPointField caused a seg-fault if the internal field was null
      - attempted to name the vtk object the name of the null field

+ minor clean-up

- the bit counting is relatively fast:
  under 0.2 seconds for 1M bits counted 1000 times

- trim()'ing the final zero elements tested for a few cases,
  but might need more attention

    - incompressible, Boussinesq variant of buoyantSimpleFoam
    - requires new fixedFluxBoussinesqBuoyantPressure bc on pd at walls
      to balance the flux generated by the temperature gradient