Added bin/otrs.SetCustomerPassword.pl

This module is for setting passwords for customer accounts, similar to
bin/otrs.SetPassword.pl.

The extra 'feature' it has is *password generation*. If you do not
specify the second argument it will generate a password for you and
set that.

If you think it is useful (I thinks so...) of course I can add this to
bin/otrs.SetPassword.pl too.