ndn.cxx: Initial work to introduce full NDN application API to ndnSIM

Refs #1005 (http://redmine.named-data.net/)
model: First set of major API changes and reorganizations

Main motive: change interface in Face class, resulting in need to change forwarding strategy interfaces

Refs #1005 (http://redmine.named-data.net/)
model: Major API changes

Interest and ContentObject are no longer derived from Header class.
Instead, they are encapsulating payload and, optionally, wire-formatted
Packet object.

Refs #1005 (http://redmine.named-data.net/)
model: Another set of refactoring/renaming to make code compile (not tested yet)

Refs #1005 (http://redmine.named-data.net/)
bindings: Rescan of python bindings

Refs #1005 (http://redmine.named-data.net/)
model+test: Fixing tests and making sure all tests pass

Refs #1005 (http://redmine.named-data.net/)
model: A basic implementation of ndn::ApiFace that can be used as an NDN handler in any "normal" NS-3 application

Refs #1005 (http://redmine.named-data.net/)
model+ndn.cxx+test: Finishing implementation of ApiFace (now timeouts are working as well)

Also, adding a basic test case to test ApiFace

Refs #1005 (http://redmine.named-data.net/)
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/)