Add Premoder to "sets do download" in image download

[pedrovgp]

When downloading images, there are predefined sets that will download images from a set of collections:

I'd like to request that collections legal in premodern be added as a set. They are many to download one by one, but the are a small share of all the images (which requires unnecessary disk space).

Alternatively, it would be nice to be able to select multiple collections. When clicking the "lupe", it allows to select multiple, but effectively that only selects the last one (which is a bit annoying).