Moving apps back to apps/ folder.  Finally worked out the problem with headers

WAF building system copies all headers to one directory. As a result,
all #include directives in all NS3 modules should be either in form
"ns3/header-file.h" or just "header-file.h", disregarding the actual
directory structure.
diff --git a/model/interest-header.h b/model/interest-header.h
index 4f2b948..9d9ba4a 100644
--- a/model/interest-header.h
+++ b/model/interest-header.h
@@ -22,8 +22,8 @@
 #ifndef _INTEREST_HEADER_H_
 #define _INTEREST_HEADER_H_
 
-#include <ns3/integer.h>
-#include <ns3/header.h>
+#include "ns3/integer.h"
+#include "ns3/header.h"
 
 #include <string>
 #include <vector>
@@ -35,7 +35,7 @@
 {
 namespace NDNabstraction
 {
-
+  
 /**
  * CCNx XML definition of Interest
  *