Stats:
```
IPv4 IPv6 Onion Pass
426728 59523 7900 Initial
426728 59523 7900 Skip entries with invalid address
426728 59523 7900 After removing duplicates
426727 59523 7900 Skip entries from suspicious hosts
123226 51785 7787 Enforce minimal number of blocks
121710 51322 7586 Require service bit 1
4706 1427 3749 Require minimum uptime
4124 1098 3681 Require a known and recent user agent
4033 1075 3681 Filter out hosts with multiple bitcoin ports
512 140 512 Look up ASNs and limit results per ASN and per net
```
Update hardcoded seeds from seeds_emzy.txt seeds_lukejr.txt
seeds_sipa.txt seeds_sjors.txt, according to release process.
Output from makeseeds.py:
```
IPv4 IPv6 Onion Pass
1364173 244127 2454 Initial
1364173 244127 2454 Skip entries with invalid address
1129552 213117 2345 After removing duplicates
1129548 213117 2345 Skip entries from suspicious hosts
338216 191944 2249 Enforce minimal number of blocks
336851 188993 2189 Require service bit 1
6998 1520 150 Require minimum uptime
5682 1290 89 Require a known and recent user agent
5622 1279 89 Filter out hosts with multiple bitcoin ports
512 146 89 Look up ASNs and limit results per ASN and per net
```
- 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
