Add styles and Jinja for component

Most of these are cut-and-paste'd from the GOVUK
metadata component:

https://components.publishing.service.gov.uk/component-guide/metadata

...but stripped back to only include what we need
and a optional suffix paragraph added.

Links to styles and ERB template
https://github.com/alphagov/govuk_publishing_components/blob/master/app/assets/stylesheets/govuk_publishing_components/components/_metadata.scss
https://github.com/alphagov/govuk_publishing_components/blob/master/app/views/govuk_publishing_components/components/_metadata.html.erb

Also adds it to the accessibility statement as an
example and updates the test that checks any
updates bump the date.

app/assets/stylesheets/components/content-metadata.scss

@@ -0,0 +1,43 @@
+.content-metadata {
+  @include govuk-font(16);
+  @include govuk-clearfix;
+  @include govuk-responsive-margin(5, "bottom");
+  color: $govuk-text-colour;
+  margin-top: 15px;
+
+  .content-metadata__term,
+  .content-metadata__definition {
+    line-height: 1.4;
+  }
+
+  .content-metadata__term {
+    margin-top: .5em;
+
+    @include govuk-media-query($from: tablet) {
+      box-sizing: border-box;
+      float: left;
+      clear: left;
+      padding-right: govuk-spacing(1);
+      margin-top: 0;
+    }
+  }
+
+  .content-metadata__definition {
+    margin: 0;
+
+    @include govuk-media-query($from: tablet) {
+      &:not(:last-of-type) {
+        margin-bottom: govuk-spacing(1);
+      }
+    }
+  }
+
+  .content-metadata__suffix {
+    margin-top: 0.628em;
+    margin-bottom: 0;
+
+    @include govuk-media-query($from: tablet) {
+      margin-top: 6px;
+    }
+  }
+}

app/assets/stylesheets/main.scss

@@ -72,6 +72,7 @@ $path: '/static/images/';
 @import 'components/loading-indicator';
 @import 'components/area-list';
 @import 'components/broadcast-message';
+@import 'components/content-metadata';
 
 @import 'views/dashboard';
 @import 'views/users';