Rewrote Credit API

- API built atop Django REST Framework
- Added support for OAuth 2.0 and session authentication
- Added permissions around eligibility data

ECOM-2609

lms/static/js/commerce/credit.js

@@ -16,6 +16,8 @@ var edx = edx || {};
             headers: {
                 'X-CSRFToken': $.cookie('csrftoken')
             },
+            dataType: 'json',
+            contentType: 'application/json',
             data: JSON.stringify({
                 'course_key': courseKey,
                 'username': username

lms/static/js/commerce/views/receipt_view.js

@@ -140,7 +140,11 @@ var edx = edx || {};
             return $.ajax({
                 url: _.sprintf(providerUrl, providerId),
                 type: 'GET',
-                dataType: 'json'
+                dataType: 'json',
+                contentType: 'application/json',
+                headers: {
+                    'X-CSRFToken': $.cookie('csrftoken')
+                }
             }).retry({times: 5, timeout: 2000, statusCodes: [404]});
         },
         /**