Recognize articles from CSV without order number

[twothreenine]

For updating articles, it can be handier to export a CSV, edit them in a spreadsheet editor, and re-import it.
However, currently, you can't use CSV export + import to edit articles in case any of the supplier's articles don't have an order number -- the first article in the list would get changed instead.

Suggestions:

• add a reference column that will be filled with the article ID that will be checked first (also useful if you want to change the order number, but keep the article)
• compare article name if neither ID nor order number is given? (for example, if you want to synchronize articles to another supplier/Foodsoft) - probably not really necessary?
• leave non-matching articles unedited (resp. delete them if the according checkbox is checked) and create new ones instead

I'd suggest to implement this after the article unit fork is merged, but before the next release, to avoid multiple breaking changes to the CSV format.