Hardcoded seeds update

Summary:
Starting from the data fetched by the seeder's crawlers
this commit will add a list of know and working BCC compliant
nodes to src/chainparamsseeds.h.

The process to follow to update the file is the following

curl -Ls https://gist.githubusercontent.com/sickpig/2c98c30ca96f19c617328bb87c00e7c0/raw/51b697c408167aba182173bf5448c7c8c5e0403e/seeds_bcc_main.txt > seeds_bcc_main
python3 ./contrib/seeds/makeseeds.py < seeds_bcc_main.txt > nodes_main.txt
touch node_tests.txt
python3 ./contrib/seeds/generate-seeds.py . > src/chainparamsseeds.h

The data fetched from the git gist is a dump of the internal list of
nodes stored by the btccash-seeder.bitcoinunlimited.info.

In the process contrib/seeds/makeseeds.py has been adapted to
handle the BCC implementations useragent (BUcash, XT, ABC and Classic)
and a bunch of filters rules has been relaxed due to the fact we
are still in the bootstrap step.

Test Plan: reproduce the changes applied to src/chainparamsseeds.h using the steps listed above

Reviewers: freetrader, deadalnix, kyuupichan, awemany, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D403