Add support for constructing VectorSpaces from forms with lower component type,
e.g. Vector<scalar> from Vector<label>

Add support for constructing VectorSpaces from forms with lower component type,
e.g. Vector<scalar> from Vector<label>

This reverts commit c5bea524.

This reverts commit b18f6cc1.

- affected: polyBoundary, fvBoundaryMesh, ZoneMesh, searchableSurfaces

  before:
      const label zoneI = mesh.cellZones().findZoneID(zoneName);
      const cellZone& cz = mesh.cellZones()[zoneI];
  after:
      const cellZone& cz = mesh.cellZones()[zoneName];

- make centrally available via #include "addOverwriteOption.H"

- ensure that the standard options (eg, from timeSelector) also have
  some usage information

- also drop various unused time options from src/OpenFOAM/include

- can use 'XX.empty()' instead of 'XX.size() == 0', 'XX.size() < 1' or
  'XX.size() <= 0' or for simpler coding.
  It also has the same number of characters as '!XX.size()' and /might/ be
  more readable

- many size checking had 'XX.size() > 0', 'XX.size() != 0', or 'XX.size() >= 1'
  when a simple 'XX.size()' suffices