Make register button for marketing site break out of iframe

Use window.top.location.href instead of location.href for redirection.

lms/templates/courseware/mktg_course_about.html

@@ -26,9 +26,9 @@
 
     $('#class_enroll_form').on('ajax:complete', function(event, xhr) {
       if(xhr.status == 200) {
-        location.href = "${reverse('dashboard')}";
+        window.top.location.href = "${reverse('dashboard')}";
       } else if (xhr.status == 403) {
-        location.href = "${reverse('register_user')}?course_id=${course.id}&enrollment_action=enroll";
+        window.top.location.href = "${reverse('register_user')}?course_id=${course.id}&enrollment_action=enroll";
       } else {
         $('#register_error').html(
             (xhr.responseText ? xhr.responseText : 'An error occurred. Please try again later.')