apps: Switch ndn::App::GetId() to use application ID on the node

Previously, GetId() used ID of the underlying application face, which
is less convenient for simulation trace analyses.

Change-Id: I403182ecb4b9e8fb010c4c25ab007c1e274bc86a
diff --git a/apps/ndn-app.hpp b/apps/ndn-app.hpp
index 57dda58..2d84134 100644
--- a/apps/ndn-app.hpp
+++ b/apps/ndn-app.hpp
@@ -85,9 +85,9 @@
   typedef void (*DataTraceCallback)(shared_ptr<const Data>, Ptr<App>, shared_ptr<Face>);
 
 protected:
-  /**
-   * @brief Do cleanup when application is destroyed
-   */
+  virtual void
+  DoInitialize();
+
   virtual void
   DoDispose();
 
@@ -101,6 +101,7 @@
 protected:
   bool m_active; ///< @brief Flag to indicate that application is active (set by StartApplication and StopApplication)
   shared_ptr<AppFace> m_face; ///< @brief automatically created application face through which application communicates
+  uint32_t m_appId;
 
   TracedCallback<shared_ptr<const Interest>, Ptr<App>, shared_ptr<Face>>
     m_receivedInterests; ///< @brief App-level trace of received Interests