Fix Inventory Unit Mapping

The orphan-removal flag is on the wrong side of the association and is discarded by doctrine.
This leads to Order::removeInventoryUnit() failing to cascade properly, and makes the cart update fail when reducing the quantity of any item in the cart. Marketing would love to keep this bug, I'm sure ;)
Add hasInventoryUnit method to Order and OrderInterface

This adds consistency between Shipment and InventoryUnit handling.
Specs are updated accordingly.
Rebuild pull request from ReadOnly SyliusFlowBundle
See https://github.com/Sylius/SyliusFlowBundle/pull/26
fronted for oauth registration
trigger FOSUserEvents::REGISTRATION_COMPLETED on oAuth based registration
comment out balance