Revisit separated footer in contained cards

Our PWA Stats cards have a footer section that's separate from the rest of the card:

Which @AriannaChau accounted for in her designs for contained cards, seen here: #1282

But because those variations represent a significant layout change that would not be used by cloudfour.com proper, I decided to delay on implementing that portion for #1287.

So this issue is a placeholder that represents revisiting that PWA Stats design element at a later date. Possible outcomes may be:

- Implementing the footer as designed in #1282
- Re-thinking the design now that we have a fresh set of patterns to work with
- Punting this design element to PWA Stats entirely