wallettool: Add dump command

Adds a new dump command to bitcoin-wallet which prints out all of the
wallet's records in hex.

src/wallet/dump.h

@@ -0,0 +1,14 @@
+// Copyright (c) 2020 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_WALLET_DUMP_H
+#define BITCOIN_WALLET_DUMP_H
+
+class CWallet;
+
+struct bilingual_str;
+
+bool DumpWallet(CWallet& wallet, bilingual_str& error);
+
+#endif // BITCOIN_WALLET_DUMP_H