We've grouped them by responsability. The responsabilities are:

- To maintain the peer lists for each torrent.
- To return the peer lists for a given torrent.
- To return the torrent entries, which contains all the info about the
  torrents, including the peer lists.
- To return the torrent metrics.
- To return the swarm metadata for a given torrent.
- To handle the persistence of the torrent entries.