BlackHole add downloading files from swarm when caching sites fail

[0x20Man]

Hi,

I prefer to use torrent file and "watch dirs" instead of magnet link but I'm having trouble with BlackHole.py downloading torrent files from caching sites, for example https://itorrents.org/ is now behind CloudFlare so it fails every time without adding "counter measures" and it's quite common to not find one using the remaining two.

I don't know if it's supported by other clients, but rTorrent can download a torrent file from the swarm using the info-hash only according to bep_0009, basically the equivalent of a magnet link in the form of a torrent file, avoiding the caching sites requirement.

The implementation is straightforward, I've created the pull request #288 if you want to add it to the main.