- provide a lookupOrDefault constructor form, since this is a fairly
  commonly used requirement and simplifies the calling sequence.

  Before

      dimensionedScalar rhoMax
      (
          dimensionedScalar::lookupOrDefault
          (
              "rhoMax",
              pimple.dict(),
              dimDensity,
              GREAT
          )
     );

  After

      dimensionedScalar rhoMax("rhoMax", dimDensity, GREAT, pimple.dict());

- read, readIfPresent methods with alternative lookup names.

- Mark the Istream related constructors with compile-time deprecated
  warnings.

BUG: read, readIfPresent methods not handling optional dimensions (#1148)