kOmegaSSTDES: New DES model based on the k-omega SST RAS model

Description
    Implementation of the k-omega-SST-DES turbulence model for
    incompressible and compressible flows.

    DES model described in:
    \verbatim
        Menter, F. R., Kuntz, M., and Langtry, R. (2003).
        Ten Years of Industrial Experience with the SST Turbulence Model.
        Turbulence, Heat and Mass Transfer 4, ed: K. Hanjalic, Y. Nagano,
        & M. Tummers, Begell House, Inc., 625 - 632.
    \endverbatim

    Optional support for zonal filtering based on F1 or F2 is provided as
    described in the paper.

    For further details of the implementation of the base k-omega-SST model
    see Foam::kOmegaSST.

    The DES coefficient 'CDES' defaults to 0.61 but may be changed as
    necessary.

    The zonal filter filter defaults to '2' which uses "(1 - F2)" as
    suggested in the paper but '0' (no filtering) and '1' which uses
    "(1 - F1)" are also supported.