Make it easier to pan images in the lightbox
Previously, if you were dragging an image and your cursor outpaced the
edge of the image as it was moving, panning would abruptly stop. This
moves a few of the lightbox event listeners one level up to the image
wrapper to ensure that all drag movements are detected, even if they
don't end over the image's current position.
Signed-off-by: Robin Townsend <robin@robin.town>
