Turn ArticleListController getBreadCrumb() into singleton call

https://www.oxid-esales.com/de/support-services/dokumentation-und-hilfe/oxid-eshop/betrieb/rabatte/artikel-als-zugabe.html

There is currently no way to add a Rabatt item only once to the basket. It works on a per line item basis.

Example:
Category food has a free spoon item associated with it. Add an article to basket you receive 1x spoon. Add another article from within the food category you receive 2x spoon.

Using the Multiplizieren checkbox will multiply it per line item amount. if you add a food item with amount 2 into your basket you receive 2x spoons. Now add another food article with amount 1 and you receive 3 spoons.

• Migration to add new field OXITSINGLETON on oxdiscount table
• Update oxBasket::_addBundles to check if item should only be added once.
• Implement singleton checkbox on admin panel discount.

Das Problem hierbei ist, dass für 13 Artikel jeweils für jeden Discount auf isForBundleItem() geprüft werden muss. Bei 67 Discounts, die in Frage kommen können macht dass dann 871 Aufrufe (37,65% gesamt), die dann über Bande und Direkt 1693 SQL Befehle an die Datenbank schickt.

First attempt worked only on products & missing categories. Oxid is also missing tests for discounts across categories.