support importing torrents

If you upload a torrent file or paste a torrent/magnet link in the import URL box, Groove Basin should download the torrent, import the music into the library, seed until the ratio is 1.5:1 or something like that with a global fixed upload rate at something like 100 KB/s. (those are defaults, obviously this would be configurable.)

https://github.com/mafintosh/torrent-stream looks pretty good.
https://github.com/feross/bittorrent-client looks good as well

yarr harr fiddle-dee-dee