ENH: Added new multiphaseStabilizedTurbulence fvOption

See GL #1433

Applies corrections to turbulence kinetic energy equation and turbulence
viscosity field for incompressible multiphase flow cases.

Turbulence kinetic energy is over-predicted in VOF solvers at the phase
interface and throughout the water column in nearly-potential flow regions
beneath surface waves.

This fvOption applies corrections based on the references:

    Buoyancy source term in turbulence kinetic energy equation:

        Devolder, B., Rauwoens, P., and Troch, P. (2017).
        Application of a buoyancy-modified k-w SST turbulence model to
        simulate wave run-up around a monopile subjected to regular waves
        using OpenFOAM.
        Coastal Engineering, 125, 81-94.

    Correction to turbulence viscosity field:

        Larsen, B.E. and Fuhrman, D.R. (2018).
        On the over-production of turbulence beneath surface waves in
        Reynolds-averaged Navier-Stokes models
        J. Fluid Mech, 853, 419-460

Example usage:

    multiphaseStabilizedTurbulence1
    {
        type            multiphaseStabilizedTurbulence;
        active          yes;

        multiphaseStabilizedTurbulenceCoeffs
        {
            // Optional coefficients
            lambda2         0.1;   // A value of 0 sets the nut correction to 0
            Cmu             0.09;  // from k-epsilon model
            C               1.51;  // model coefficient from k-omega model
            alpha           1.36;  // 1/Prt
        }
    }

Thanks go to the Turbulence Technical Committee, and the useful discussions
with and code testing by Bjarke Eltard-Larsen and David Fuhrman (Technical
University of Denmark).