functionObjects::scalarTransport: Added support for MULES with sub-cycling and semi-implicit options

Description
    Evolves a passive scalar transport equation.

    - To specify the field name set the \c field entry
    - To employ the same numerical schemes as another field set
      the \c schemesField entry,
    - The \c diffusivity entry can be set to \c none, \c constant, \c viscosity
    - A constant diffusivity is specified with the \c D entry,
    - If a momentum transport model is available and the \c viscosity
      diffusivety option specified an effective diffusivity may be constructed
      from the laminar and turbulent viscosities using the diffusivity
      coefficients \c alphal and \c alphat:
      \verbatim
          D = alphal*nu + alphat*nut
      \endverbatim

    Example:
    \verbatim
        #includeFunc scalarTransport(T, alphaD=1, alphaDt=1)
    \endverbatim

    For incompressible flow the passive scalar may optionally be solved with the
    MULES limiter and sub-cycling or semi-implicit in order to maintain
    boundedness, particularly if a compressive, PLIC or MPLIC convection
    scheme is used.

    Example:
    \verbatim
        #includeFunc scalarTransport(tracer, diffusion=none)

    with scheme specification:
        div(phi,tracer)     Gauss interfaceCompression vanLeer 1;

    and solver specification:
        tracer
        {
            nCorr      1;
            nSubCycles 3;

            MULESCorr       no;
            nLimiterIter    5;
            applyPrevCorr   yes;

            solver          smoothSolver;
            smoother        symGaussSeidel;
            tolerance       1e-8;
            relTol          0;

            diffusion
            {
                solver          smoothSolver;
                smoother        symGaussSeidel;
                tolerance       1e-8;
                relTol          0;
            }
        }
    \endverbatim

tutorials/incompressible/pimpleFoam/RAS/flowWithOpenBoundary/system/controlDict

@@ -45,7 +45,7 @@ runTimeModifiable true;
 
 functions
 {
-    #includeFunc scalarTransport(T, alphaD=1, alphaDt=1)
+    #includeFunc scalarTransport(T, alphal=1, alphat=1)
     #includeFunc time
 }