Add cookie banner text, page, and footer links

> Let’s start the footer links with the cookie page.
> Banner to say: "GOV.UK Notify uses cookies to make the site simpler. Find out
> more about cookies"
> Standard style one... see
> https://www.registertovote.service.gov.uk/register-to-vote/cookies or
> https://www.digitalmarketplace.service.gov.uk/cookies
>
> Let's link to the feedback form too...
> https://docs.google.com/forms/d/1AL8U-xJX_HAFEiQiJszGQw0PcEaEUnYATSntEghNDGo/viewform
> Call it Support and feedback

https://www.pivotaltracker.com/story/show/115483375

app/assets/stylesheets/_grids.scss

@@ -30,3 +30,19 @@
   padding-left: 2px;
   padding-right: 2px;
 }
+
+.global-cookie-message {
+  p {
+    @extend %site-width-container;
+  }
+}
+
+.footer-nav {
+  @include copy-16;
+  margin-bottom: $gutter-two-thirds;
+
+  a {
+    display: inline-block;
+    margin-right: $gutter-half;
+  }
+}

app/assets/stylesheets/app.scss

@@ -80,3 +80,11 @@ a {
   }
 
 }
+
+td {
+  vertical-align: top;
+}
+
+.heading-xlarge {
+  margin-bottom: 20px;
+}