Download .torrent files and add them to database

[zypA13510]

In my database, I can see many torrents that are bundles of a whole lot of other torrent files. As an indexer, the ability to "follow these links" to index the pieces' data contained within might make sense.

Of course, there are some risks, as this effectively requires that we download the pieces for analysis, which is very different from downloading only metadata - pieces whose legality we cannot ascertain, not until finishing the download at least. It makes sense to limit this function to download torrents that contain only torrent files (plus paddings #166), and probably as an opt-in feature. Alternatively, provide a setting to limit downloads to only those where .torrent files exceed a certain percentage in size or in the number of files.

There is also the question of whether we should seed after downloading this data, as some of these bundles have several GBs of torrents, and because leeching is bad.

Not a priority, just an idea for future development.