Feat/webpack (#2998)

* First commit

* Removed govuk for webpack. Modernized javascript importing. Removed dead js

* Fixed tests, a few styling bugs

* Fixed some table errors and regenerated backstop ref images

* Updated tests for coverage

* Changes from carlo suggestions

app/assets/javascripts/errorBanner.js

@@ -1,16 +1,7 @@
-(function (window) {
-  "use strict";
+export const ErrorBanner = {
+  hideBanner: () => $('.banner-dangerous').addClass('display-none'),
+  showBanner: () => $('.banner-dangerous').removeClass('display-none')
+};
 
-  /*
-  This module is intended to be used to show and hide an error banner based on a javascript trigger. You should make
-  sure the banner has an appropriate aria-live attribute, and a tabindex of -1 so that screenreaders and keyboard users
-  are alerted to the change respectively.
-
-  This may behave in unexpected ways if you have more than one element with the `banner-dangerous` class on your page.
-  */
-  window.NotifyModules.ErrorBanner = {
-    hideBanner: () => $('.banner-dangerous').addClass('display-none'),
-    showBanner: () => $('.banner-dangerous')
-      .removeClass('display-none')
-  };
-})(window);
+window.NotifyModules = window.NotifyModules || {};
+window.NotifyModules.ErrorBanner = ErrorBanner;