Added currency form type and validator
merged branch mvrhov/currency (PR #6566)

This PR was merged into the master branch.

Discussion
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[2.3] Added currency locale data, form type and validator

Bug fix: no
Feature addition: yes
Backwards compatibility break: no
Symfony2 tests pass: yes
License of the code: MIT
Documentation PR: symfony/symfony-docs#2105

Commits
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5609aae Added currency form type and validator