added notebook for testing/demonstrating Qobj.extract_states and Qobj.eliminate_states
added notebook for testing/demonstrating Qobj.extract_states and Qobj.eliminate_states

zasdfgbnm/qutip,zasdfgbnm/qutip,cgranade/qutip,qutip/qutip,cgranade/qutip,anubhavvardhan/qutip,qutip/qutip,anubhavvardhan/qutip