Add axial offset option for creating a volume from a h5 file

[gschlafly]

The function BirefringentVolume.create_dummy_volume contains a parameter to shift the volume axially by a given amount. It would be great if this option were also added to BirefringentVolume.init_from_file. These functions are located in VolumeRaytraceLFM\birefringence_implementations.py.

[pvjosue]

Good idea. We briefly talked about this with Grant.
A more elegant way of doing this would be to create a 'translate', 'rotate', 'scale' functions, such that we can translate not only axially but in any direction, and we could transform and create more complex volumes without overloading the init_from_file function.

If you agree I' can implement these functions :)

[gschlafly]

I agree—much more elegant!