Support for Bitgesell (BGL) coin

[van-orton]

Add support for Bitgesell (BGL) coin.

Notes: It is BTC-derived, main noteworthy differences are:

• Tx hashes and block hashes are SHA3-Keccak;
• All transactions should be segwit and addresses bech32/BIP0173;
• 90% of tx fees are burned (this and few other differences are not relevant for integration);
• Great btcd/btcutil golang repositories were forked to keep things separated (just in case);
• The node is 100% compatible with Bitcoin Core commands, JSON-RPC API and config file options/cmdline args;

Tests look green. As well as there are probably code/configuration changes required in other repositories.
We would gladly answer questions or make requested changes.

[wu-emma]

Hi @loongy @jazg ! How're you? Could we help with something from our side? We are pretty sure that BGL could be integrated smoothly (very much compatible with BTC) and the code is working.
We could ask BGL community to participate and we also could ask them to support this initiative if you provide a wallet address.

[janus]

Hello Team, I am a dev with Bithesell(BGL). We're waiting for the feedback and could you provide some information on how we can achieve progress with the integration? We are getting some traction and network awareness. We moved past our first halving recently and community grows too, we are looking forward our cooperation.

[wu-emma]

Hi guys, just a ping!
if anything, we're ready to refactor resolve merge conflicts.