Use QUDT as data source for UN/ECE units

[lentschi]

Adapt UN/ECE data source, so they use QUDT in addition - see https://forum.foodcoops.at/t/foodsoft-artikeleinheiten-hackerton-start-fixieren/5951/77

[lentschi]

... or WikiData @paroga
e.g.: https://www.wikidata.org/wiki/Q11570

[lentschi]

@paroga Since you're generally "off the grid": Do you have any plans of implementing this issue soon?

Otherwise I'd just stick with the direct imports from https://datahub.io/ while applying a fix to address the one relevant issue with that mentioned in the forum.

(The remaining issues #10 and #18 are blocked by this issue, so I need to finally address it. We should still be able to replace the direct import with QUDT in a separate MR later if required.)

[lentschi]

Closing this and sticking with the direct imports as suggested