This reverts merge request !841

- sourced out duplicate code

Preserve body structure in send_notification_email

Add new file 100-monitor_kernel_version.inc.php to stable-3.1 in relation to recently merged commits of !790 and !791.

There is a fix to the filename for master submitted via commit !804 that is still pending.

Missed .inc in filename 100-monitor-kernel-version.php

Add new file to display current kernel info. Related to comment ispconfig/ispconfig3!789 (comment 63987)

Update letsencrypt.inc.php as per the discussion at ispconfig/ispconfig3#5030. Already pr'ed and merged in master via ispconfig/ispconfig3!778. Perhaps can be merged with stable too?

ispconfig/ispconfig3#5030

Added a third parameter to $app->log() function in server part to turn off logging to database and use this option in mysql lib to not log any server side SQL errors to the database.

Make traffic quota datas available for template