ENH: Jump conditions - added optional minimum jump value

Example:

    plane
    {
        type            fan;
        patchType       cyclic;
        jump            uniform 0;
        value           uniform 0;
        uniformJump     false;

        relax           0.2;

        jumpTable       ( (1000 0) (-200 1) (20 2) (-0.75 3) );

        // Optional minimum jump value
        minJump         0;
    }