ENH: Q.groundstate now checks for degeneracy.
ENH: Q.groundstate now checks for degeneracy.

- Groundstate now calculates the lowest two states and checks to see if
they are possibly degenerate and warns the user to use Q.eigenstates()
instead.

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