Fix #815, Use timedatectl to modify system time zone

Created by: JoKeyser

This should fix #815 (closed). Thank you for the good explanation how to implement it. Let me know if something needs adjustment.

Created by: SunilMohanAdapa

Merged with very minor changes. Thanks for the patch.

Please try to match the style of your commit messages with the project style (see earlier commits). I had one minor issue during testing and I raised it a as separate pull request in #827 (up for review by you).

Created by: JoKeyser

Great, thanks. Will watch out for the commit messages from now on, thanks for the heads-up. Will look at #827 later, I'm interested.