Adding support of more fields in ContentObject

All big fields (digest, signature, etc.) are represented with 32-bit
integers. Should be enough for simulation purposes.

Also. This commit contains a number of code reorganizations, so the code
may not work...
diff --git a/helper/ccnb-parser/visitors/ccnb-parser-interest-visitor.cc b/helper/ccnb-parser/visitors/ccnb-parser-interest-visitor.cc
index b7ccaba..ff219f0 100644
--- a/helper/ccnb-parser/visitors/ccnb-parser-interest-visitor.cc
+++ b/helper/ccnb-parser/visitors/ccnb-parser-interest-visitor.cc
@@ -32,7 +32,7 @@
 #include "ccnb-parser-name-components-visitor.h"
 #include "ccnb-parser-non-negative-integer-visitor.h"
 #include "ccnb-parser-timestamp-visitor.h"
-#include "ccnb-parser-nonce-visitor.h"
+#include "ccnb-parser-uint32t-blob-visitor.h"
 
 #include <boost/foreach.hpp>
 
@@ -53,7 +53,7 @@
   static NonNegativeIntegerVisitor nonNegativeIntegerVisitor;
   static NameComponentsVisitor     nameComponentsVisitor;
   static TimestampVisitor          timestampVisitor;
-  static NonceVisitor              nonceVisitor;
+  static Uint32tBlobVisitor        nonceVisitor;
   
   CcnxInterestHeader &interest = *(boost::any_cast<CcnxInterestHeader*> (param));