Allow to download multiple articles at once (see below)
Allow to download multiple articles at once (see below)

It is now possible to download articles based on
 - their article number
 - their url
 - whether they are known already

Known articles and article numbers that do not identify an article are
stored so that known articles do not need to be downloaded again.

Some hacks are introduced to cope with PD issues.

kopp/ebookvoice,kopp/ebookvoice