Session token and signature isn't presented in `Container` and
`EACLTable` messages of NeoFS API V2 protocol. These entities are needed
for access control and doesn't carry payload of these messages.
Remove `SetSessionToken` / `SessionToken` methods of
`container.Container` and `eacl.Table` types. Provide methods to specify
these components in corresponding `Client` operations.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Remove `signature` and `util/signature` packages. Re-implement their
functionality in new `crypto` package. Generalize the approach of
digital signature computation and verification by adding `Signer` and
`PublicKey` primitives similar to standard `crypto` package. Support
already exising in protocol signature schemes.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
