Use the new wizard for all imports (even if no Mendeley DB), and add a
page with a "Place imported collections and items into new collection"
option. If deselected, collections are added to the library root.
If there's a single PDF file and a single PDF URL and the file exists,
make an imported_url attachment instead of separate file and linked_url
attachments.
Addresses #1451
Accept Mendeley SQLite databases via File → Import… and perform a
direct import, including collections, timestamps, notes, attachments,
and extracted annotations.
When a Mendeley database is present, File → Import… shows a wizard that
lets you choose between a file and Mendeley for the source, and choosing
the latter shows a list of available databases in the Mendeley data
directory.
Known fields that aren't valid for a type are stored in Extra.
Files in the Mendeley 'Downloaded' folder are stored. Files elsewhere
are linked.
