ENH: atmosphericModels: Added Lopes da Costa porosity and turbulence models

Specialized variants of the power law porosity and k epsilon turbulence models
developed to simulate atmospheric flow over forested and non-forested complex
terrain.

Class
    Foam::powerLawLopesdaCosta

Description
    Variant of the power law porosity model with spatially varying
    drag coefficient

    given by:

        \f[
            S = -\rho C_d \Sigma |U|^{(C_1 - 1)} U
        \f]

    where
    \vartable
        \Sigma | Porosity surface area per unit volume
        C_d    | Model linear coefficient
        C_1    | Model exponent coefficient
    \endvartable

    Reference:
    \verbatim
        Costa, J. C. P. L. D. (2007).
        Atmospheric flow over forested and non-forested complex terrain.
    \endverbatim

Class
    Foam::RASModels::kEpsilonLopesdaCosta

Description
    Variant of the standard k-epsilon turbulence model with additional source
    terms to handle the changes in turbulence in porous regions represented by
    the powerLawLopesdaCosta porosity model.

    Reference:
    \verbatim
        Costa, J. C. P. L. D. (2007).
        Atmospheric flow over forested and non-forested complex terrain.
    \endverbatim

    The default model coefficients are
    \verbatim
        kEpsilonLopesdaCostaCoeffs
        {
            Cmu         0.09;
            C1          1.44;
            C2          1.92;
            sigmak      1.0;
            sigmaEps    1.3;
        }
    \endverbatim

Tutorial case to follow.