Fix challenge sorting

Closes #7543
Closes #7507

website/server/controllers/api-v3/challenges.js

@@ -201,7 +201,7 @@ api.leaveChallenge = {
  * @apiName GetUserChallenges
  * @apiGroup Challenge
  *
- * @apiSuccess {Array} data An array of challenges
+ * @apiSuccess {Array} data An array of challenges sorted with official challenges first, followed by the challenges in order from newest to oldest
  */
 api.getUserChallenges = {
   method: 'GET',
@@ -218,7 +218,7 @@ api.getUserChallenges = {
       ],
       _id: {$ne: '95533e05-1ff9-4e46-970b-d77219f199e9'}, // remove the Spread the Word Challenge for now, will revisit when we fix the closing-challenge bug TODO revisit
     })
-    .sort('-official -timestamp')
+    .sort('-official -createdAt')
     // see below why we're not using populate
     // .populate('group', basicGroupFields)
     // .populate('leader', nameFields)
@@ -249,7 +249,7 @@ api.getUserChallenges = {
  *
  * @apiParam {groupId} groupId The group _id
  *
- * @apiSuccess {Array} data An array of challenges
+ * @apiSuccess {Array} data An array of challenges sorted with official challenges first, followed by the challenges in order from newest to oldest
  */
 api.getGroupChallenges = {
   method: 'GET',
@@ -268,7 +268,7 @@ api.getGroupChallenges = {
     if (!group) throw new NotFound(res.t('groupNotFound'));
 
     let challenges = await Challenge.find({group: groupId})
-      .sort('-official -timestamp')
+      .sort('-official -createdAt')
       // .populate('leader', nameFields) // Only populate the leader as the group is implicit
       .exec();