Rework Get Involved rendering for GOVUK Component System

The Frontend team removed many functions being used in the original port
of this page from Whitehall. This commit updates the page to fit the
component ecosystem from govuk_publishing_components with the added
benefit of losing a lot of now unnecessary CSS content for the same
end result.

app/assets/stylesheets/application.scss

@@ -8,8 +8,10 @@ $govuk-new-link-styles: true;
 @import 'govuk_publishing_components/govuk_frontend_support';
 @import 'govuk_publishing_components/components/attachment';
 @import 'govuk_publishing_components/components/back-link';
+@import 'govuk_publishing_components/components/big-number';
 @import 'govuk_publishing_components/components/breadcrumbs';
 @import 'govuk_publishing_components/components/button';
+@import 'govuk_publishing_components/component_support';
 @import 'govuk_publishing_components/components/contents-list';
 @import 'govuk_publishing_components/components/contextual-sidebar';
 @import 'govuk_publishing_components/components/details';
@@ -23,6 +25,7 @@ $govuk-new-link-styles: true;
 @import 'govuk_publishing_components/components/govspeak-html-publication';
 @import 'govuk_publishing_components/components/heading';
 @import 'govuk_publishing_components/components/hint';
+@import 'govuk_publishing_components/components/image-card';
 @import 'govuk_publishing_components/components/input';
 @import 'govuk_publishing_components/components/intervention';
 @import 'govuk_publishing_components/components/inverse-header';
@@ -91,8 +94,6 @@ $govuk-new-link-styles: true;
 @import 'views/help-page';
 @import 'views/guide';
 @import 'views/get-involved';
-@import 'views/headings';
-@import 'helpers/featured_news';
 
 .travel-advice-notice {
   background-color: govuk-colour("light-grey");