Handle weight and percentage both being specified

[wvengen]

Sometimes both a percentage and a weight is specified, maybe we need to support both:

Double chocolate cookiemix 400 g (89,9%): TARWEbloem [GLUTEN], suiker, palmolie, zonnebloemolie, glucosestroop, magere cacaopoeder 7,2%, KIPHEELEIpoeder (scharrel), MELKeiwit, GERSTemoutbloem [GLUTEN], zout, rijsmiddelen: E500-E450, aroma. Witte chocolade chunks 45 g (10,1%): suiker, volle MELKpoeder, cacaoboter, emulgator: SOJAlecithine, aroma.

[wvengen]

We could recognize both percentage and amount, where a new attribute 'percentage' contains the percentage, and the existing attribute 'amount' is about weight or volume (breaking change, though). I haven't seen both weight and volume specified, so this should be ok.