model+ndn.cxx+apps: New application template (CallbackBasedApp) that can be used to prototype NS-3 applications in python

The current code allows simulating in python using ApiFace (passed basic tests)

Refs #1005 (http://redmine.named-data.net/)
diff --git a/wscript b/wscript
index 9407508..eaa54c2 100644
--- a/wscript
+++ b/wscript
@@ -153,6 +153,7 @@
         "utils/ndn-rtt-estimator.h",
 
         "ndn.cxx/ndn-api-face.h",
+        "apps/callback-based-app.h",
         ]
 
     if 'topology' in bld.env['NDN_plugins']: