Stable 3.1

Add checkbox to main config for show/hide backup tab in mail account details.

See merge request !451

Fixed #4173 No SSL Tab for client if SSL available but also Let\'s Encrypt available template limit is active.

How to reproduce issue

[Added] username_error_regex to en_web_folder_user.lng

Added an error message

See merge request !450

Fixed typo en_ftp_user.lng

fixed a little typo

See merge request !449

Fixes #4189



See merge request !448

DNSSEC-Cronjob should only run on ispconfig master as we are working with datalo…

…g and not accessing things directly

@tbrehm, am I right that `$app->db->datalogUpdate`for a soa on the ispc master does also update the dns_soa table in master database or do I have to do this by hand?
This could probably be a reason for the issue of @jnorell in #1491 ...

See merge request !446

Fix updater appsvhost config

closes ispconfig/ispconfig3#4177

See merge request !447

fixed code styling (bit of a perfectionist) - Looks like someone accidentially removed an if clause here before and fixing killed styling.

Mlmmj web interface implementation

I've tried to implement  an ISPConfig interface for Mlmmj
There are only some params implemented for now
I've tried to create a user friendly interface and not a simple GUI for all Mlmmj TUNABLES!

See merge request !439

DNSSEC-Cronjob should only run on ispconfig master as we are working with datalog and not accessing things directly

Make sure admin check apply to all admins and not just user 1.

Make sure admin check apply to all admins and not just user 1.

See merge request !443