rpc: Register calls where they are defined

Split out methods to every module, apart from 'help' and 'stop' which
are implemented in rpcserver.cpp itself.

- This makes it easier to add or remove RPC commands - no longer everything that includes
    rpcserver.h has to be rebuilt when there's a change there.
- Cleans up `rpc/server.h` by getting rid of the huge cluttered list of function definitions.
- Removes most of the bitcoin-specific code from rpcserver.cpp and .h.

Continues #7307 for the non-wallet.

src/rpc/register.h

@@ -0,0 +1,32 @@
+// Copyright (c) 2009-2016 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_RPCREGISTER_H
+#define BITCOIN_RPCREGISTER_H
+
+/** These are in one header file to avoid creating tons of single-function
+ * headers for everything under src/rpc/ */
+class CRPCTable;
+
+/** Register block chain RPC commands */
+void RegisterBlockchainRPCCommands(CRPCTable &tableRPC);
+/** Register P2P networking RPC commands */
+void RegisterNetRPCCommands(CRPCTable &tableRPC);
+/** Register miscellaneous RPC commands */
+void RegisterMiscRPCCommands(CRPCTable &tableRPC);
+/** Register mining RPC commands */
+void RegisterMiningRPCCommands(CRPCTable &tableRPC);
+/** Register raw transaction RPC commands */
+void RegisterRawTransactionRPCCommands(CRPCTable &tableRPC);
+
+static inline void RegisterAllCoreRPCCommands(CRPCTable &tableRPC)
+{
+    RegisterBlockchainRPCCommands(tableRPC);
+    RegisterNetRPCCommands(tableRPC);
+    RegisterMiscRPCCommands(tableRPC);
+    RegisterMiningRPCCommands(tableRPC);
+    RegisterRawTransactionRPCCommands(tableRPC);
+}
+
+#endif