Add MCIP-6 Byzyantium transition to Musicoin spec (#7841)

* Add test chain spec for musicoin byzantium testnet

* Add MCIP-6 Byzyantium transition to Musicoin spec

* Update mcip6_byz.json

* ethcore: update musicoin byzantium block number

* ethcore: update musicoin byzantium block number

* ethcore: update musicoin bootnodes

* Update musicoin.json

* Update musicoin.json

* More bootnodes.