Categorize rpc help overview

Conflicts:
	src/rpcserver.cpp

Github-Pull: #4539
Rebased-By: Wladimir J. van der Laan <laanwj@gmail.com>
Rebased-From: df3d321

src/rpcserver.h

@@ -71,6 +71,7 @@ typedef json_spirit::Value(*rpcfn_type)(const json_spirit::Array& params, bool f
 class CRPCCommand
 {
 public:
+    std::string category;
     std::string name;
     rpcfn_type actor;
     bool okSafeMode;