
Update witness properties for the given account.

Parameters:
    witness_name: The name of the witness account. (type: const string &)
    url: A URL containing some information about the witness. The empty
	string makes it remain the same. (type: const string &)
    block_signing_key: The new block signing public key. The empty string
	disables block production. (type: public_key_type)
    props: The chain properties the witness is voting on. (type: const
	wallet_serializer_wrapper<legacy_chain_properties> &)
    broadcast: true if you wish to broadcast the transaction. (type: bool)
