Add a planar illumination geometry

[RecurvedBow]

Please describe your :rocket: feature request. As a developer who is unfamiliar with the effects of lighting on simulations, I want to define a global light that evenly illuminates the entire tissue to compare different lighting conditions.

Describe the solution you'd like The ideal solution would be to define a planar illumination geometry.

Describe alternatives you've considered An alternative would be to define a PencilArrayIlluminationGeometry with an illuminator defined for each voxel, however, this might not illuminate all spots evenly compared to a planar illumination geometry.

[faberno]

I have already worked on this, can open a PR soon.

[RecurvedBow]

Sorry, I did not see your comment & have just implemented it, but we can combine our implementations into one single feature.