Stable 3.1

See merge request !812

copy MySQL client flags support from master

See merge request ispconfig/ispconfig3!813

This reverts commit c97bed44.

This reverts commit 0933e169.

This reverts commit ff16ebc2.

Show server hostname under system > server config (#5063)

See merge request ispconfig/ispconfig3!800

Fixed connection issue in mail account import tool.

Add word "Kernel" to respective language files

See merge request ispconfig/ispconfig3!808

Update show_sys_state.php to display current kernel info.

See merge request ispconfig/ispconfig3!806

Add new file 100-monitor_kernel_version.inc.php to stable-3.1

See merge request ispconfig/ispconfig3!805

Add word "Kernel" to all respective language files in stable3.1.

$wb['monitor_serverstate_kernel_txt'] = 'Kernel';

In relation with the earlier merged commits of !790 
 and !791.