added back energy_level_diagram functions that seems to have gone missing
added back energy_level_diagram functions that seems to have gone missing

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