daemon: mark some classes and methods 'final'

As suggested by gcc's -Wsuggest-final-types and -Wsuggest-final-methods

Change-Id: I1622857ee53581efd0c6ce3fe93199c72202d817
diff --git a/daemon/mgmt/face-manager.hpp b/daemon/mgmt/face-manager.hpp
index c1547c5..db2e5aa 100644
--- a/daemon/mgmt/face-manager.hpp
+++ b/daemon/mgmt/face-manager.hpp
@@ -36,7 +36,7 @@
  * @brief Implements the Face Management of NFD Management Protocol.
  * @sa https://redmine.named-data.net/projects/nfd/wiki/FaceMgmt
  */
-class FaceManager : public ManagerBase
+class FaceManager final : public ManagerBase
 {
 public:
   FaceManager(FaceSystem& faceSystem,