This backward compatible change allows wallets/dapps to add additional
features outside the basic transaction signature support to the
hdwalletv1 protocol.
Allows dapps to cache the raw PathXpub[] from wallet_ready and restore
them on subsequent page loads. restoreSessionPaths decodes the xpub strings
and populates pubkeyState so getPubkey() works without waiting for the
wallet to reconnect. Throws on invalid xpub data.
