Streaming downloads #1565
Description
On slow connections (i.e., mine), for large files, flask's send_from_directory will timeout before the full file is downloaded by the user.
To start with we can probably be more generous with our gnicorn timeouts to allow larger downloads to squeeze through, or more robustly, we can switch to streaming file rather than simply send_from_directory, would need to test the content types etc. that this works for but could be an option explicitly for files larger than a few GB.