Add AB testing setup for July 2016 session

This commit sets up AB test for the following smart answers:

* overseas-passport
* calculate-your-child-maintenance
* marriage-abroad

Cohorts across the aforementioned smart answers fall under the following.

* Start now
* Continue
* Next

app/assets/javascripts/smart-answers.js

@@ -1,7 +1,13 @@
+//= require start-button-ab-test-july-2016
+
 function browserSupportsHtml5HistoryApi() {
   return !! (history && history.replaceState && history.pushState);
 }
 
+function isExpectedPath(slug) { // Used mostly during A/B testing
+  return window.location.pathname.split("/").join("") == slug;
+}
+
 $(document).ready(function() {
   if(browserSupportsHtml5HistoryApi()) {
     var formSelector = ".current form";

app/assets/javascripts/start-button-ab-test-july-2016.js

@@ -0,0 +1,48 @@
+//= require govuk/multivariate-test
+
+$(function(){
+  if(isExpectedPath("overseas-passports")) {
+    new GOVUK.MultivariateTest({
+      el: '.get-started a',
+      name: 'startButton_osPassport_201607',
+      customDimensionIndex: [13, 14],
+      cookieDuration: 2, // set cookie expiry to 2 days
+      contentExperimentId: 'cZbCgQy3SOCHEX2l6bU-eQ',
+      cohorts: {
+        original: { callback: function() {}, variantId: 0},
+        next: { html: 'Next', variantId: 1 },
+        continue: { html: 'Continue', variantId: 2 }
+      }
+    });
+  }
+
+  if(isExpectedPath("calculate-your-child-maintenance")) {
+    new GOVUK.MultivariateTest({
+      el: '.get-started a',
+      name: 'startButton_calcChildM_201607',
+      customDimensionIndex: [13, 14],
+      cookieDuration: 2, // set cookie expiry to 2 days
+      contentExperimentId: '02HyTKtNR-yHsYlI6JoJqg',
+      cohorts: {
+        original: { callback: function() {}, variantId: 0},
+        next: { html: 'Next', variantId: 1 },
+        continue: { html: 'Continue', variantId: 2 }
+      }
+    });
+  }
+
+  if(isExpectedPath("marriage-abroad")) {
+    new GOVUK.MultivariateTest({
+      el: '.get-started a',
+      name: 'startButton_marriageAbroad_201607',
+      customDimensionIndex: [13, 14],
+      cookieDuration: 2, // set cookie expiry to 2 days
+      contentExperimentId: 'ABoraDMOQCC9WjJWsTpIPg',
+      cohorts: {
+        original: { callback: function() {}, variantId: 0},
+        next: { html: 'Next', variantId: 1 },
+        continue: { html: 'Continue', variantId: 2 }
+      }
+    });
+  }
+});