Renamed unitary_matrix() to propogators()
Renamed unitary_matrix() to propogators()

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