Coordinates of points `point_set_from_points_layer` appear reverted

[N-Dekker]

It appears that the coordinates of the points of an itk::PointSet returned by point_set_from_points_layer are in reverse order.

More specifically, when retrieving the points returned by point_set_from_points_layer, their coordinates still need to be reverted before passing them as "fixed_points" or "moving_points" to itk.elastix_registration_method.

• Observed when implementing pull request ENH: Support napari layers of corresponding points SuperElastix/elastix-napari#65

@thewtex Can you please have a look?

[thewtex]

@N-Dekker 👍 please take a look at #15