Upgrade NeoFS API Go library to version with status returns. Make all API
clients to pull out and return errors from failed statuses. Make signature
service to respond with status if client version supports it.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Replace UnaryHandler from structure to method arguments in order to reuse
single instance for different service methods.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
