Fixed #4425 Variable is initialized as string but later written to as array, throws fatal error in PHP 7.1

Improved the code that generates the ssh keys for clients and shell users and reorganized it into a central function.

Datalogstatus notification implementation (as discussed: https://www.howtoforge.com/community/threads/datalogstatus.73719/)

Fixed #4057 Remote API: some API calls are not working because the form definition files are missing

Fixed #2738 Installing package from APS to root of subdomain fails when/if. Thanks to @gardan for the patch.

Fixed #4043 3.1 Remote API - client_add: sys_user insert fails if client parameter 'usertheme' is empty