This commit continues on work laid out by 6039b513fe to redesign the /about page. In this commit, we add the site age and a section on the right hand side to show site activities/statistics such as topics, posts, sign-ups, likes etc.
This commit introduces the foundation for a new design for the /about page that we're currently working on. The current version will remain available and still be the default until we finish the new version and are ready to roll out. To opt into the new version right now, add one or more group to the `experimental_redesigned_about_page_groups` site setting and members in those groups will get the new version.
Internal topic: t/128545.
Run `prettier --write "app/assets/stylesheets/**/*.scss" "plugins/**/*.scss"` after making sure you installed it with `yarn`
It's recommended to configure your editor to run prettier on file save.
