add checkbox cross off effect to challenges and reword pairwise bonfire

public/css/main.less

@@ -910,6 +910,10 @@ iframe.iphone {
   text-decoration: underline;
 }
 
+.step-text {
+  margin-left: -10px;
+}
+
 //uncomment this to see the dimensions of all elements outlined in red
 //* {
 //  border-color: red;

public/js/main.js

@@ -30,6 +30,15 @@ $(document).ready(function() {
       .addClass('animated fadeInDown');
   });
 
+  $('.challenge-list-checkbox').on('change', function() {
+    if ($(this).is(":checked")) {
+      $(this).parent().parent().children('.step-text').addClass('strikethrough text-primary');
+    }
+    if (!$(this).is(":checked")) {
+      $(this).parent().parent().children('.step-text').removeClass('strikethrough text-primary');
+    }
+  });
+
   function completedBonfire(didCompleteWith, bonfireSolution, thisBonfireHash, bonfireName) {
     $('#complete-bonfire-dialog').modal('show');
     // Only post to server if there is an authenticated user