Api v3 Migration (WIP) (#7131)

* v3 migration: remove old code and polish user migration

* v3 migration: start to work on challenges

* wip v3 migration

* wip v3 migration: fix _id -> id for reminders, tags and checklists

common/script/libs/taskDefaults.js

@@ -23,7 +23,7 @@ module.exports = function taskDefaults (task = {}) {
     value: task.type === 'reward' ? 10 : 0,
     priority: 1,
     challenge: {},
-    reminders: {},
+    reminders: [],
     attribute: 'str',
     createdAt: new Date(), // TODO these are going to be overwritten by the server...
     updatedAt: new Date(),