The relay descriptor downloader so far only downloads server and
extra-info descriptors that are referenced in other directory documents
and that we are missing.
With this patch we also download /tor/server/all and /tor/extra/all from
the directories once per day to learn about server and extra-info
descriptors that are not referenced anywhere.
This patch further requests the compressed versions of descriptors by
adding ".z" to the URLs in order to save bandwidth.
This patch is a 50% rewrite of the relay descriptor downloader which
became too complex over time.
There's no need to maintain a local file with dirreq stats only to import
the same data to the database shortly after. We now import to the
database directly in RelayDescriptorDatabaseImporter.
We once needed to mantain different GeoIP database versions to resolve
bridge IP addresses to country codes in the sanitizing process. We gave
up on that, because it was too complex. That means we don't need the
GeoIP database manager anymore. If we decide we need it, it'll live on in
Git's history.
