Proposal: Generalize Multi-pages images support

[Elad-Laufer]

Instead of the current approach of trying to handle multipage images in each function in a specific way, or declaring the operation not supported we can consider the following:

1. On the first operation that requires specific handling of pages, break a multipage image in to multiple images and hold them in a slice under ImageRef
2. Apply the operation to each image independently
3. On consecutive operations, if the slice exist continue applying them independently
4. On export, Join the images back into a roll and then export the result - unless the target format does not support animation and in this case default to the first frame (add frame selection option?)

[Elad-Laufer]

NOTE: How does holding multiple imageRef (one per page) affect memory pressure?