CSV export can show NaN for date if TimeZone does not match system

[ddb4github]

Describe the bug

Graph CSV export all data as NaA with wrong date range if browser timezone is different with web server

To Reproduce

1. Configure web server timezone as EST(-05:00), Browser side timezone is CST(+08:00)
2. Create a new graph, ensure its valid data timerange is less than 13 hours
3. Access Graphs-->Preview
4. Select "Last 4 Hours"
5. Compare params in href of "csv export", and timespans
   layout.js -->getTimestampFromDate() convert timespan date1/date2 to timestamp with browser local timezone
6. Click "csv export" icon, and check csv file

"Start Date","2020-11-23 10:37:00"
"End Date","2020-11-23 14:37:00"
.......
"2020-11-23 15:04:00","NaN","NaN"

Screenshots

Additional context

Maybe, global_session.php can output web server timezone info as JS variables

[TheWitness]

Have you considered a pull request for this @ddb4github?

[TheWitness]

Resolved @ddb4github. Please verify.

[TheWitness]

@ddb4github, based upon your comments, I have reworked this changes a little to ensure that all timestamps in the web site align with the browser as well. Please validate and provide feedback. This does not change the CLI's.