This PR also includes the string changes in #3459, but if that is approved first I'll drop them from here. To see just the design changes, you can view this diff.

• Style the headers on all 4 About subpages with the new artwork. This does mess up the dashboard widget, there's another ticket for that.
• Update the icons in the grid, adding the missing ones and some cleanup.
• Add the screenshots, using temporary make/core URLs in case they change. These will be added to s.w.org CDN when final.
• Updates some spacing and typography to match the design

Links to the screenshots, because they're very big: About, Credits, Freedoms, Privacy

And in other languages: Arabic (RTL), Korean, Swedish

Trac ticket: https://core.trac.wordpress.org/ticket/56357

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.