Add case_sensitive option for confirmation validation

    Case :- 1. In case of email confirmation one needs case insensitive comparison
            2. In case of password confirmation one needs case sensitive comparison
@zzak  I think at present we have limited the validation of confirmation for password confirmation. Leaving the scope for others. Moreover we are currently following the same pattern with uniqueness validation already. So it will not be a big change. What's your thought?
Should I close this PR?