ENH: fanFvPatchField - refactored; added flowRate option

The basis of the table is specified according to the mode:

- velocity: deltap = F(velocity per face) \[DEFAULT\]
- uniformVelocity: deltap = F(patch area-averaged velocity)
- volumeFlowRate:  deltap = F(patch volume flow rate)
- nonDimensional:  non-dim deltap = F(non-dim volume flow rate)

Example of the boundary condition specification:

    <patchName>
    {
        type            fan;
        patchType       cyclic;
        jumpTable       csvFile;
        mode            velocity; // New entry

        jumpTableCoeffs
        {
            nHeaderLine     1;
            refColumn       0;
            componentColumns 1(1);
            separator       ",";
            mergeSeparators no;
            file            "<constant>/UvsPressure";
        }
        value           uniform 0;
    }