better cooperation with external MPI initialize / finalize

See merge request OpenFOAM-plus!252

- change from UpdateableMeshObject to TopologicalMeshObject

- change inheritance order to have MeshObject be registered first
  and mark the IOobject descriptor as unregistered

- the objectRegistry destructor seems to be called too late.
  Explicitly clear the objectRegistry within the Time destructor to
  ensure that it always happens.

This reverts commit 708e6509.

- used fallback of 0 instead of the results time.
  This discrepancy caused the case file to have two timesets that
  only differed by the first (incorrect) entry.

- when running in serial but within a processor directory,
  argList::globalPath() is to be used instead of Time.globalPath()
  For other cases there is no difference.

- silence clang warnings

- this is somewhat like labelRange, but with a stride.
  Can be used to define slices (of lists, fields, ..) or as a range specifier
  for a for-loop. For example,

      for (label i : sliceRange(0, 10, 3))
      {
          ...
      }

- removed unused decrement() and increment() methods, which provided
  identical functionality as the ++, +=, --, -= operators.

Adding pMin,Pmax pressure control to buoyantPimple and
chtMultiReagion

- with the wmake rules we may have some compiler options bound to the
  internal compiler variable. For example,

     CC  = g++ -std=c++11 -m64

     c++FLAGS = ...

  So shift any flags from CC to CXXFLAGS for the output of
  'wmake -show-cxx', 'wmake -show-cxxflags', etc.

  This makes it much easier to handle the values correctly elsewhere.
  Eg,

      CXX="$(wmake -show-cxx)" CXXFLAGS="$(wmake -show-cxxflags)" \
         ./configure

- provide dedicated detection 'have_ptscotch' function that can be
  used after the 'have_scotch' function.

  It sets the PTSCOTCH_ARCH_PATH, PTSCOTCH_INC_DIR, PTSCOTCH_LIB_DIR
  and helps when the serial and parallel versions are located with
  different logic.

- the writer nFields() is a separate type of accounting (currently
  only needed by VTK legacy) and is independent of the geometry.

- still had old WM_PROJECT_VERSION settings instead of FOAM_API
  for FOAM_SITE_APPBIN and FOAM_SITE_LIBBIN locations.

oversetInterpolationSuppressed dict.

- file-local static for saving the old action, which moves system
  dependencies out of the header files.

- set/reset of signals as file-local functions

STYLE: use csignal header instead of signal.h

- this improves overall consistency and is independent of higher level
  tagging as ASCII or BINARY for IFstream, OFstream etc.

- this adds support for various STL operations including

    * sorting, filling, find min/max element etc.
    * for-range iteration

STYLE: use constexpr for VectorSpace rank

- consistent with use of <cstdlib> and makes for a stronger distinct
  from Foam::abort etc.

- this improves overall consistency and makes re-reading as a generic
  patch field behave properly when the underlying patch has zero size.