fvOptions: The "<type>Coeffs" sub-dictionary is now optional

For example the actuationDiskSource fvOption may now be specified

disk1
{
    type            actuationDiskSource;

    fields      (U);

    selectionMode   cellSet;
    cellSet         actuationDisk1;
    diskDir         (1 0 0);    // Orientation of the disk
    Cp              0.386;
    Ct              0.58;
    diskArea        40;
    upstreamPoint   (581849 4785810 1065);
}

rather than

disk1
{
    type            actuationDiskSource;
    active          on;

    actuationDiskSourceCoeffs
    {
        fields      (U);

        selectionMode   cellSet;
        cellSet         actuationDisk1;
        diskDir         (1 0 0);    // Orientation of the disk
        Cp              0.386;
        Ct              0.58;
        diskArea        40;
        upstreamPoint   (581849 4785810 1065);
    }
}

but this form is supported for backward compatibility.