Fix dragging of files to the filesystem on macOS (and maybe Linux)
Fix dragging of files to the filesystem on macOS (and maybe Linux)

Calling getTransferData('zotero/item') when handling the
application/x-moz-file-promise seems to have stopped working between Fx46 and
Fx47, though I can't get older Nightly builds to run with mozregression
(Sierra?) to find the specific change. Instead, work around this by passing an
array of item ids to the file drag data provider.

gracile-fr/zotero,gracile-fr/zotero,gracile-fr/zotero