Make start date and day of month aware of timezones (fixes #12555) (#12696)

* WIP: #12555

-dayOfMonth takes timezone into account on task update for monthly dailys
-startDate set to start of day in user's tz on task update for monthly
dailys
-tweaked a test so that it's actually testing something

* WIP: 12555

-task.startDate gets set to start of day in user's tz on task creation
and task update
-set preferences.timezoneOffset to nonzero value in certian test user objects
-removed date literals in test:api-v3:integration:tasks:PUT

website/server/models/task.js

@@ -378,7 +378,7 @@ export const DailySchema = new Schema(_.defaults({
   startDate: {
     $type: Date,
     default () {
-      return moment().startOf('day').toDate();
+      return moment.utc().toDate();
     },
     required: true,
   },