Packing of multiview images working

Notes:
* This will pack multiple images if the format is R_IMF_VIEWS_INDIVIDUAL
* When packing as PNG we convert the views_format to R_IMF_VIEWS_INDIVIDUAL
* Technically we could use the same principle to pack a sequence of images (with some changes of course, since this approach relies on ImageView
Image Editor saving of image in 3d (individual views) working

Note: I need to go over this function again to see if I'm handling the
'save as copy' == false correctly. If the image is saved to a
descructive format, in that case we should change the current image (and
I'm almost sure I overlooked that).

This function can likely be simplified as well now that I'm more
comfortable with the whole image pipeline.