Update email signup forms

[brandon-rusk]

Changes

• Updated the email signup forms across https://cfpb.github.io/

Screenshots

[chosak]

Code changes look good to me, but two minor things:

• In the internal issue, @sonnakim mentions for the footer "Ignore spacing in screenshot below — the left-hand side should take up 50% of the width, not 33%." When I test this locally (and on your fork's GHP) I see the width as 33%.
• Instead of duplicating the GovDelivery URL in several different places, could we define a new Jekyll variable and refer to it that way? I believe we'd have to edit our _config.yml file to add the new variable; see the docs for site.[CONFIGURATION_DATA] here. So we could define something like mailing_list_url: <url_here> and then in templates refer to {{ site.mailing_list_url }}.