fvOptions::limitVelocity: New fvOption to limit the maximum velocity magnitude

e.g. to avoid excessive unphysical velocities generated during slamming events in
incompressible VoF simulations

Usage
    Example usage:
    limitU
    {
        type            limitVelocity;
        active          yes;

        limitVelocityCoeffs
        {
            selectionMode   all;
            max             100;
        }
    }