Make it store its internal `zap.Logger`'s level. Also, make all the
components to accept internal `logger.Logger` instead of `zap.Logger`; it
will simplify future refactor.
Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>
Add `WithEncryption` option that passes ECDSA key to the persistent session
storage. It uses 32 bytes from marshalled ECDSA key in ASN.1 DER from in
AES-256 algorithm encryption in Galois/Counter Mode.
Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>
