da48e4ba1e
This adds `srcset` and `sizes` to the about page images, including art direction, via `<picture>` for the lead Twenty Seventeen image. This also replaces URLs for all images and feature videos to their CDN locations on s.w.org. Props helen, pento, joemcgill. Fixes #38616. Built from https://develop.svn.wordpress.org/trunk@39514 git-svn-id: http://core.svn.wordpress.org/trunk@39454 1a063a9b-81f0-0310-95a4-ce76da25c4cd