* enable optional cumulation of multiple regular vouchers (overruling best option rule) // fix bug where vouchers could falsely be cumulated when pricerule is identical // add unit tests
* fix pre-filtering of vouchers
* minor cleanup
* refactor: remove access to global test data from promo cumulation tests // add test for employee disscount
* feat: ExcludeAlreadyDiscountedItemsForVoucher does no longer apply to discounts with TypePromotionCustomer
* update unit tests for promo cumulation
* update unit tests for promo cumulation
* update pricerule cumulation tests
* pricerules: reimplement test for BuyXPayY
* add more tests for pricerules