Implement `IsOwner` and `IDEquals` functions which check the
correspondence of the fields in `Info`. Remove no longer needed
`HasOwner` method of `Info`.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Create `subnet` package. Define `Info` type of the subnet info. Support
encoding and transport over the NeoFS API V2 protocol. Add methods to
work with identifier and owner.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
