Make it so that ImageFrame operations return an ImageFrame, same as CIFrame #4
Description
Therefore, if I compute the residuals of a CIFrame, the residuals should also be a CIFrame and therefore have access to the frame_geometry / ci_pattern attributes and methods.
This is currently implemented (I think), but not using array_filnalize in the classes, which makes it a lot cleaner.
Furthermore, the add_cti_to_image / correct_cti_from_image routines in CTIImage should return images that are instaces of the ImageFrame class.