This change allows us to refactor the shopping-card to have its ratings
case without needing to duplicate the card widget itself. Additionally,
this will allow us to use the card widget for the translations case in
about:preferences.
The button styles in moz-card.css will need to be de-duplicated in the
future, once we figure out the moz-button widget.
Differential Revision: https://phabricator.services.mozilla.com/D187712
a204bb5e6f