Update the steps for updating the hardcoded seed nodes to point to the
new filename on @sipa's server, and add command to decompress it.
Ref: #10163
Github-Pull: #10495
Rebased-From: ac9cd953d91e2448d24851b2f4973c7be8f4c3cd
- 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