Add multiple items via import

[Dan Stillman]

For standard multi-item responses, I think it's fine to have the user select a single item. This isn't Zotero, and there's really no reason to use search result pages, so the user likely wants a single item.

With /import, though, the calling site has specifically passed a page or file to import, and in that case it seems like we should prompt to add all provided items instead of selecting one. We can then either skip the review box or, if it's easy, show a review box for all added items.

This will allow a site to provide multiple items selected via checkboxes or "my library" features.

[Dan Stillman]

Test URL: https://gist.githubusercontent.com/adam3smith/4105816/raw/423844f41879f2754fe2affa94f8a76a5b7b5efd/sample.ris