New Weber number cloud function object

Example usage:

cloudFunctions
{
    WeberNumber1
    {
        type    WeberNumber;
    }
}

This will calculate and write the Weber number field as a 'standard' cloud field, available for post-processing alongside other lagrangian fields in the lagrangian/ directory.

See example in $FOAM_TUTORIALS/lagrangian/sprayFoam/aachenBomb/constant/sprayCloudProperties