Implement blog/article theming with new card type and layout options

This is ready for review.

• - Created a library for basic pages, page.basic, where basic body elements and blockquotes are styled. This library can be used to update or override styles for all body or content-driven pages.
• - Comments now have a dedicated library definition and are fully themed and styled.
• - Article pages are styled with two new container sizes—very narrow and narrow—to better display content. Both pages are styled to match the designs.
• - Added a reusable date badge class with full styling.
• - Applied badge classes to article tag fields.
• - Created a new card type, card--basic, themed and styled according to the designs, and applied it to article teasers.
• - Added new bust-out mixin to display full-width background color outside the section container.
• - Added CSS variable for footer margin with defaults.

Working on this to shift changes from #3522433 🐛 There should be some space between tow articles Active and #3494468 🐛 Tags needs space from bottom. Active .

The whitespace beneath tags is clearly visible now. These screenshots are related to #3494468 🐛 Tags needs space from bottom. Active

The whitespace between articles on the home page is clearly visible now. These screenshots are related to #3522433 🐛 There should be some space between tow articles Active .

Working for me, there is now white space at the bottom of content pages

The code has been merged. This issue is now resolved. Thanks everyone for the help and testing!