model: Updated API for pluggable wire format

As of this commit, the selected (default) wire format is controlled via
global variable ndn::WireFormat:

    Config::SetGlobal ("ndn::WireFormat", IntegerValue (ndn::Wire::WIRE_FORMAT_CCNB));

or

    ./waf --run="... --ndn::WireFormat=1

Refs #1008 (http://redmine.named-data.net/issues/1008)
diff --git a/wscript b/wscript
index b33da18..ff2b7f3 100644
--- a/wscript
+++ b/wscript
@@ -150,8 +150,7 @@
         "model/fw/ndn-forwarding-strategy.h",
         "model/fw/ndn-fw-tag.h",
 
-        "model/wire/ndnsim.h",
-        "model/wire/ccnb.h",
+        "model/wire/ndn-wire.h",
 
         "utils/ndn-limits.h",
         "utils/ndn-rtt-estimator.h",