Product Alternatives - by algorithm

[bobslee]

While issue #36 already describes the "Product alternatives" by manual assignment.
This feature could also be implemented (automatically) by an algorithm/program.
Likewise alternatives could be queried by matching on Product criteria/properties like for example:

• Items in a Category tree which are flagged as "specific/matchable"
• Product Variants etc.

Therefor these requirements need te be implemented first.