On keyboard interrupt in the regular flow of downloading the collected images of this session and of last session are saved so as not to destroy the archive accidentally this way.
If an item is added to the new collection, it is removed from the old one.
If a save is being dumped (uncleanly saved because of KB interrupt), the old collection is appended to the new one.
Upon loading the returned string is split to enable removing of the old items.
Using kirbybase to store downloaded images
A nasty bug that always returned the wrong result when checking whether an image had already been downloaded has been fixed
