Wanted feature

[d47081]

The conception is in allow to users download wanted torrents and become Yggdrasil seeders.

This feature also makes any torrent uploaded accessible to download it by others using local network.

Details in Wiki

• [x] Clickable "Wanted" label to download raw file with all announcements required (Yggdrasil and regular ones)
• [x] Update scrapper crontab task that generates wanted torrent files (with all trackers) in /var/torrents/wanted dir
• [x] Create read-only FTP mirror to setup remote access for third-party bittorrent client scanners
• [x] Activity event support
• [x] Wiki description