- Use a FL token when available
- Added a configuration (default off) to enable the feature
- Skip prefetching the data with Deluge as with Transmission in
`preprocess()`
- Note: because QBittorrent & uTorrent need the data to compute the
torrenthash but still require the url to download the file, it will
result in 2 FL tokens used instead of one because the .torrent will be
downloaded twice from the server.
Fixes#3163