rib: remote prefix registration

resolve 3 bugs:

There are redundant registrations/unregistrations if loading the
config file multiple times.

Remote registration/unregistration will fail if localhop_security
is enabled.

Unstable RemoteRegistrator/UnregisterAdvanced test case.

Change-Id: I4437292e9f6c0e340c761ef7556a9bdc703ac06c
refs: #2294
diff --git a/rib/rib.hpp b/rib/rib.hpp
index ed9ca4e..2568b1a 100644
--- a/rib/rib.hpp
+++ b/rib/rib.hpp
@@ -30,6 +30,7 @@
 #include "fib-update.hpp"
 #include "common.hpp"
 #include <ndn-cxx/management/nfd-control-command.hpp>
+#include <ndn-cxx/util/signal.hpp>
 
 namespace nfd {
 namespace rib {
@@ -137,8 +138,8 @@
   removeInheritedFacesFromEntry(RibEntry& entry, const Rib::FaceSet& facesToRemove);
 
 public:
-  ndn::util::EventEmitter<Name> afterInsertEntry;
-  ndn::util::EventEmitter<Name> afterEraseEntry;
+  ndn::util::signal::Signal<Rib, Name> afterInsertEntry;
+  ndn::util::signal::Signal<Rib, Name> afterEraseEntry;
 
 private:
   RibTable m_rib;