change CASNumberCheckDigit and ECNumberCheckDigit, add ECIndexNumberValidator

[homebeaver]

routines in package org.apache.commons.validator.routines.checkdigit do not validate the input for length or syntax. This is documented in package-info

Respected this idea I change CASNumberCheckDigit and ECNumberCheckDigit.

And provide CASNumberValidator and ECNumberValidator which validates the syntax.

I also add a Validator for ECIndexNumber, a unique nine-digit identifier that is assigned to hazardous chemical substances.

regards EUGen