Stable 3.1

See merge request ispconfig/ispconfig3!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 !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.

Update show_sys_state.php to display current kernel info for stable-3.1 in relation to recently merged commits of ispconfig/ispconfig3!790 and ispconfig/ispconfig3!791.

There is a fix to the filename for master submitted via commit ispconfig/ispconfig3!804 that is still pending.

Add new file 100-monitor_kernel_version.inc.php to stable-3.1 in relation to recently merged commits of ispconfig/ispconfig3!790 and ispconfig/ispconfig3!791.

There is a fix to the filename for master submitted via commit ispconfig/ispconfig3!804 that is still pending.

mail routing configuration allows every server to be selected (Fixes #5068)

See merge request ispconfig/ispconfig3!799

MySQL connect with client flags. Fixes #4558

See merge request ispconfig/ispconfig3!798