57 wigner distribution

[EthanMcGarrigle-SNL]

Adds a Wigner distribution W(x,p) calculation method into the State class, which returns the Wigner distribution for every mode in the state over its position and momentum degrees of freedom. The calculation itself is done using qutip methods. A test in "test_state.py" was added to test this functionality, which also tests tracing out degrees of freedom.

• added quadrature expectations computation, e.g. x, p, x^2, p^2, as a method in state to compute those expectation values for all motional modes in the basis. There is an option not to compute and return <x^2> and <p^2>.
• added X, P operators into named operators Fock class
• added a test for computing the quadrature expectation values in test_state.py.
• In the basis class, set aside property methods for "spin_DOFs" and "motional_DOFs". This is helpful in the State methods for easy retrieval of the spin or motional DOFs.
• In the state class, created a property method to return the motional state from a general State object. It either returns a State with a purely motional basis or "None" if there are no motional mode DOFs in the original state. This traces out any spin DOFs if they're present.