[Validator] Added IBAN validator

Validation for International Bank Account Numbers
merged branch sprain/validator-iban (PR #6677)

This PR was merged into the master branch.

Discussion
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[Form] [Validator] Added IBAN validator

Bug fix: no
Feature addition: yes
Backwards compatibility break: no
License of the code: MIT

Validation for International Bank Account Numbers
http://en.wikipedia.org/wiki/International_Bank_Account_Number

I don't know if the community likes new validators. I have been using this in many projects and would love to see it integrated directly with Symfony.

Commits
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c8906f4 [Validator] Added IBAN validator
[Validator] fixed CS