Make the click-a11y script callable

[pyrello]

Resolves #856.

Also, as part of this work, the headline component was updated to not include properties related to the content containing a link or not. Since the inclusion of the link doesn't have any affect on how the headline gets styled, we can just let the headline component be a wrapper around whatever text or link gets inserted into and avoid having the extra logic related to applying properties based on the link.

To test

Using https://uids.brand.uiowa.edu/branches/callable_click_a11y/ to test:

• Check card examples against https://uids.brand.uiowa.edu/latest/ to see if there are any regressions.
• Confirm that unlinked card is not linked: https://uids.brand.uiowa.edu/branches/callable_click_a11y/?path=/story/components-card--with-no-link

[pyrello]

Updated summary to reflect the changes to the headline component. Shouldn't affect testing instructions, since the headline is included in the card and will get tested as part of testing the cards.