Allow for non-8333 nodes to appear in the internal seeds. This will
allow bitcoind to bypas a filter on 8333. This also makes it possible to
use the same tool for e.g. testnet.
As hosts with multiple nodes per IP are likely abusive, add a filter to
remove these (the ASN check will take care of them for IPv4, but not
IPv6 or onion).
- Moved all seed related scripts to contrib/seeds for consistency
- Updated `makeseeds.py` to handle IPv6 and onions, fix regular
expression for recent Bitcoin Core versions
- Fixed a bug in `generate-seeds.py` with regard to IPv6 parsing
