The seeders now produce onion and i2p seeds, so there is no need to keep these
in the manual list.
Although should also be produced, there are not enough
good ones detected by the seeder, so we keep the manual seeds for them.
- 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