Only load images on demand #4519
Description
Is your feature request related to a problem? Please describe.
I have a document with more than 300 images. Even on a fast connection it takes very long to load the whole document because all images are loaded before the editor is ready.
Describe the solution you'd like
Images should only be loaded when they are visible.
Describe alternatives you've considered
Make the editor ready before all images are loaded would also work. I think it's better to not load all images at once to save some network bandwith.
Additional context
A bit related to #4242, but not the same problem.