Add FreeProduct promotion
Add FreeProductAction specs
Rename promotion and fix feedbacks
Fix typo during rebase
Use new DataTransformer
Add translation
Use VariantRepository to reduce SQL queries
Fix TaxonomyRuleChecker

Items in cart are not inventory units
Implement revert method
Make use of OrderItem::equals
Add behat scenario
Merge pull request #698 from winzou/freeproduct-promotion

[Promotion] Add FreeProduct promotion