RPC calls for background daemon added in

The RPC calls the daemon executable uses to talk to the running daemon
instance have mostly been added back in.  Rate limiting has not been
added in upstream, but is on its way in a separate effort, so those
calls are still NOPed out.

src/cryptonote_core/cryptonote_core.cpp

@@ -110,6 +110,11 @@ namespace cryptonote
     return res;
   }
   //-----------------------------------------------------------------------------------
+  void core::stop()
+  {
+    graceful_exit();
+  }
+  //-----------------------------------------------------------------------------------
   void core::init_options(boost::program_options::options_description& /*desc*/)
   {
   }