Initializes the chain from the genesis header.

def from_genesis_header(cls,
                            base_db: BaseDB,
                            genesis_header: BlockHeader) -> 'BaseHeaderChain':
        """
        Initializes the chain from the genesis header.
        """
        headerdb = cls.get_headerdb_class()(cast(BaseAtomicDB, base_db))
        headerdb.persist_header(genesis_header)
        return cls(base_db, genesis_header)