Implement `AddKeys` / `RemoveKeys` methods to call `addKey` / `removeKey`
methods of NeoFS ID contract.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Implement NeoFS ID contact's client which is responsible for collecting call
arguments and parsing stack items. Initially only key listing method is
supported.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>