Update user roles in store after owner transfer

Closes #3466
- Transferring the owner role is now done via a separate
  endpoint and not through Ember-Data.  As a result the
  user role data needs to be updated manually.
- Updated the owner endpoint to return a response body
  containing the updated user objects.
- Updated tests.

ghost/admin/controllers/modals/transfer-owner.js

@@ -14,7 +14,18 @@ var TransferOwnerController = Ember.Controller.extend({
                         'id': user.get('id')
                     }]
                 }
-            }).then(function () {
+            }).then(function (response) {
+                // manually update the roles for the users that just changed roles
+                // because store.pushPayload is not working with embedded relations
+                if (response && Ember.isArray(response.users)) {
+                    response.users.forEach(function (userJSON) {
+                        var user = self.store.getById('user', userJSON.id),
+                            role = self.store.getById('role', userJSON.roles[0].id);
+
+                        user.set('role', role);
+                    });
+                }
+
                 self.notifications.closePassive();
                 self.notifications.showSuccess('Ownership successfully transferred to ' + user.get('name'));
             }).catch(function (error) {