Draft: window: Add a page for comparing orginal and upscaled images
This adds a new page that will show the original image on the left, and upscaled image on right. The amount on which image is shown can be changed using the slider in the middle of the page. The page also allows for zooming into the image, and going back/forth the queue of upscaled images using touchpad gestures, on screen buttons, and keyboard commands. It also fits into the current accent colour and style.