rTorrent: Delete Torrent Directories

This should remove directories of torrents safely, this only removes the directories on torrents flagged as 'multi-file', checks the torrent directory ends with the directory name of the torrent to ensure we don't have the root somehow and only removes directories that are empty (as the files should be removed on #L215)

I'm not able to test this as I don't have a working setup with rTorrent, @jkaberg could you check this?