Multi-file download endpoint (book manager)
is blocked by #588 (closed)
We need a new REST endpoint for downloading files associated with a book, that
- receives the book id & an array of chapter ids as input
- for each chapter we need to create a folder, named as the chapter's BCMS id, for the latest versions of its files (its contents and structure should be identical to having selected all for a chapter as described in #588 (closed))
- all the folders should be put in a zip file, named as the book's BCMS id
- nested structures (ie. chapters being nested under parts should be ignored)
The endpoint should have a simple unit test that we can run, as the UI for this doesn't exist (yet).