Feature: #619 - Add BeVariantInterface and ProductInterface
See Issue 619
Description
To make the extension even more flexible, only the interfaces for Products and
Be are to be used in the shopping cart. This makes it easier to replace
them with your own implementations of the interfaces.
Furthermore, for Products, Be and Fe corresponding
Factories and FactoryInterfaces should offer the possibility to customize the
products in the shopping cart even easier with own Factories.
Impact
No direct impact. XCLASSing for products, BeVariants and FeVariants should no longer be necessary. Instead, separate classes should implement the corresponding interfaces.