#231 Add a transformation between adiabatic and diabatic states

[Ulf Lorenz]

What and Why

For propagation, the diabatic representation is usually better, but the "natural" basis is always adiabatic. Implement a transformation that can transform between the two.

Note: The general problem is AFAIR hard. Maybe a oe- or two-dimensional transformation would already by good enough.

Note: Having a transformation for Floquet states would be neat. There, we usually start in the diabatic representation, which is much simpler.