Include a maximum number of articles to be sold

[yksflip]

feature request by ardjan

the Adam fork already included an option to include a maximum number of products to be sold in the regular product upload/ordering system. Now we are improvising with the Stock functionality to achieve the same functionality, but that is quite cumbersome.

Should be already in here somewhere: https://github.com/foodcoop-adam/foodsoft

[yksflip]

foodcoop-adam@0ac5c9c