Wannier and Atomic Gauge

[stevenbos123]

I would like to have methods that transform back and forth from the Wannier to the Hamilton gauge.
In docs\wannier_basis.md you find the formulas that need to be implemented.
In wann_utils.py I already implemented those formulas.
The task is to check that those routines are correct and optimize them

[stevenbos123]

@rreho do you have more details on why we needs this and how this can be implemented? If not relevant we can put it in the fridge

[rreho]

I think this is a core functionality for a code that should handle Wannier IO.