Credit message on track selection page.

* Adds a credit course mode to indicate that a course
has a credit option.

* Hides the credit option from the track selection and
pay-and-verify pages.

* Shows different messaging for the verified track if
it's possible to upgrade from verified to credit at the end
of the course.

common/djangoapps/course_modes/views.py

@@ -96,9 +96,24 @@ class ChooseModeView(View):
         chosen_price = donation_for_course.get(unicode(course_key), None)
 
         course = modulestore().get_course(course_key)
+
+        # When a credit mode is available, students will be given the option
+        # to upgrade from a verified mode to a credit mode at the end of the course.
+        # This allows students who have completed photo verification to be eligible
+        # for univerity credit.
+        # Since credit isn't one of the selectable options on the track selection page,
+        # we need to check *all* available course modes in order to determine whether
+        # a credit mode is available.  If so, then we show slightly different messaging
+        # for the verified track.
+        has_credit_upsell = any(
+            CourseMode.is_credit_mode(mode) for mode
+            in CourseMode.modes_for_course(course_key, only_selectable=False)
+        )
+
         context = {
             "course_modes_choose_url": reverse("course_modes_choose", kwargs={'course_id': course_key.to_deprecated_string()}),
             "modes": modes,
+            "has_credit_upsell": has_credit_upsell,
             "course_name": course.display_name_with_default,
             "course_org": course.display_org_with_default,
             "course_num": course.display_number_with_default,