Add btdigg backend

A resubmit of the previous one, this time with understandable name.
Copied the original submission text.

This is a simple backend for btdigg.org. This site is especially
interesting because it is not an indexer where uploaders add their
torrents; it crawls the DHT and listens to all infohashes being
exchanged by the nodes.

Because of this, btdigg.org provides no description and no torrent
files, only magnets. Moreover, there are no seeders and leechers
(although there is the number of peers in the swarms)

Note that there is no icon.

Signed-off-by: Matthieu Rakotojaona <matthieu.rakotojaona@gmail.com>
Signed-off-by: Romain Bignon <romain@symlink.me>
the 12-25 card has been removed
rename bitedick to btdigg
use weboob.tools.misc.get_bytes_size
introduce Matthieu Rakotojaona
Make GPG ignore local settings
GPG keys: use minimal exports

Otherwise building the keyring can fail because it cannot find
some of the keys.