Extends ProductPrice plugin to handle selection products correctly
Important: The order product ID is now the ID of the parent product of a selection while the product code is still the code of the article
Implements selection client in catalog detail view for product variants
Additionally, fixes a problem in the basket controller with incomplete and non-unique variant attributes when checking selection products
Adapts the unit test data and the dependent tests in the catalog index manager tests
Makes sure only prices with list type "default" are used
Adapts to renamed config decorator
Allow to have multiple items with different types.
Fixes missing rename of MemoryCache config decorator
Revert "Allow to have multiple items with different types."

This reverts commit e96e10503583ee1262431901a0e13d14502176fb.
Merge pull request #254 from nsendetzky/master

Implements selection client in catalog detail view for product variants