Add tool for generating dataplane traces
Undo accidental commit of dart_pox and pox_carp
Refactor Host, HostInterface, Link into abstract classes

This refactoring allows to have multiple implementatinos for the same entities.
control_flow_test.py will fail because of this change. This is due to pickle
unable to load the new classes. It will be fixed in later commits.
Import style changes to keep things consistent
some refactoring to make pylint happy
Add deprecated decorator

Helps with identifying unused code. Copied from python's website
https://wiki.python.org/moin/PythonDecoratorLibrary
Add SSHEntity

Add parant entity for things controlled via SSH
Add missing unit test for SSHEntity

Forgot to include this in the previous commit
Refactor controllers entities

- Move controller code to a single file
- Add tests (unit and integration) for controllers
- Use SSHEntity as a base for VMController