Update cookies page

Includes:
- new content
- added option to turn analytics on/off
- non-js version for the on/off switch
- a banner to confirm user's choice was saved,
  shown when they click the save button
- the cookie banner that appears on all other
  pages removed from this page

app/assets/javascripts/cookieSettings.js

@@ -0,0 +1,84 @@
+window.GOVUK = window.GOVUK || {};
+window.GOVUK.Modules = window.GOVUK.Modules || {};
+
+(function (Modules) {
+  function CookieSettings () {}
+
+  CookieSettings.prototype.start = function ($module) {
+    this.$module = $module[0];
+
+    this.$module.submitSettingsForm = this.submitSettingsForm.bind(this);
+
+    document.querySelector('form[data-module=cookie-settings]')
+      .addEventListener('submit', this.$module.submitSettingsForm);
+
+    this.setInitialFormValues();
+  };
+
+  CookieSettings.prototype.setInitialFormValues = function () {
+    var currentConsentCookie = window.GOVUK.getConsentCookie('consent');
+
+    if (!currentConsentCookie) { return; }
+
+    var radioButton;
+
+    if (currentConsentCookie.analytics) {
+      radioButton = document.querySelector('input[name=cookies-analytics][value=on]');
+    } else {
+      radioButton = document.querySelector('input[name=cookies-analytics][value=off]');
+    }
+
+    radioButton.checked = true;
+  };
+
+  CookieSettings.prototype.submitSettingsForm = function (event) {
+    event.preventDefault();
+
+    var formInputs = event.target.querySelectorAll("input[name=cookies-analytics]");
+    var options = {};
+
+    for ( var i = 0; i < formInputs.length; i++ ) {
+      var input = formInputs[i];
+      if (input.checked) {
+        var value = input.value === "on" ? true : false;
+
+        options.analytics = value;
+        break;
+      }
+    }
+
+    window.GOVUK.setConsentCookie(options);
+
+    this.showConfirmationMessage();
+
+    if(window.GOVUK.hasConsentFor('analytics')) {
+      window.GOVUK.initAnalytics();
+    }
+
+    return false;
+  };
+
+  CookieSettings.prototype.showConfirmationMessage = function () {
+    var confirmationMessage = document.querySelector('div[data-cookie-confirmation]');
+    var previousPageLink = document.querySelector('.cookie-settings__prev-page');
+    var referrer = CookieSettings.prototype.getReferrerLink();
+
+    document.body.scrollTop = document.documentElement.scrollTop = 0;
+
+    if (referrer && referrer !== document.location.pathname) {
+      previousPageLink.href = referrer;
+      previousPageLink.style.display = "block";
+    } else {
+      previousPageLink.style.display = "none";
+    }
+
+    confirmationMessage.style.display = "block";
+  };
+
+  CookieSettings.prototype.getReferrerLink = function () {
+    return document.referrer ? new URL(document.referrer).pathname : false;
+  };
+
+  Modules.CookieSettings = CookieSettings;
+})(window.GOVUK.Modules);
+