Image Lazy Loading

[moebrowne]

This PR adds lazy loading to images site wide

[tdelmas]

Thank you for that contribution.

Could you add a comment with more information about:

• Why this change is useful
• Where/When loading="lazy" should be added

As I see it, it may be useful for pages with a lot of small images outside of the screen on the first load, or for pages with heavy images, right?
Or is it better to apply it to every images?

Documentation: https://developer.mozilla.org/en-US/docs/Web/Performance/Lazy_loading#Images_and_iframes

Also, the build fail because the html validator apparently doesn't know that tag: validator/validator#811
That must be solved one way or another.

According to https://developer.mozilla.org/en-US/docs/Web/HTML/Element/img most modern browsers support the loading attribute.

[tdelmas]

Thank you again @moebrowne for your contribution. I've open #1355 to automatically add loading=lazy to the content of all pages (not the full page, only then content).

I'll close this PR but do not hesitate to comment again here or on the other.