Initializes the chain from the genesis header.

def from_genesis_header(cls,
                            base_db: BaseAtomicDB,
                            genesis_header: BlockHeader) -> 'BaseChain':
        """
        Initializes the chain from the genesis header.
        """
        chaindb = cls.get_chaindb_class()(base_db)
        chaindb.persist_header(genesis_header)
        return cls(base_db)