[payum][paypal] add suppor of instant notifactions.
fix comments.
fix notify order action class.
Use ResourceDataTransformer

and redude hard dependency
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
fix sync request not supported.
Implement revert method
Add easy way to disable inventory tracking.

Currently inventory is always being tracked (resulting in backorders if not replenished).
This PR adds a simple NoopInventoryOperator and a configuration switch.
Run all specs at once
Make use of OrderItem::equals
Add behat scenario
Move forms from Promotion to Code
Remove CountryToIdentifierType