core: drop std::function and ndn::Exclude from common.hpp, add ndn::optional

Change-Id: Ie3983d8b6f9929430efd8ada8d942e3f95755cd4
diff --git a/tools/nfdc/cs-module.hpp b/tools/nfdc/cs-module.hpp
index 320ce09..4181290 100644
--- a/tools/nfdc/cs-module.hpp
+++ b/tools/nfdc/cs-module.hpp
@@ -53,7 +53,7 @@
 
   void
   fetchStatus(Controller& controller,
-              const function<void()>& onSuccess,
+              const std::function<void()>& onSuccess,
               const Controller::DatasetFailCallback& onFailure,
               const CommandOptions& options) override;