Container can be created within a session, and should be signed.
Add `SessionToken` / `SetSessionToken` (`Signature` / `SetSignature`)
methods to carry session token (signature) in `Container` structure.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Implement NonceUUID/SetNonceUUID methods on container structure. Change
implementation of Nonce/SetNonce methods and mark them deprecated.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
