Update aps_guicontroller.inc.php - fixed lookup for dbserver of client

See merge request ispconfig/ispconfig3!715

Fix #4931 Allow underscore in cron domain names

See merge request !717

Full translate.

See merge request ispconfig/ispconfig3!716

If db server is now a webserver, explode list of db_servers and choose first of list.

Update simplepie.inc.php

See merge request ispconfig/ispconfig3!714

Update simplepie.inc.php

See merge request ispconfig/ispconfig3!712

Update cron.inc.php

See merge request ispconfig/ispconfig3!710

Update 100-monitor_openvz.inc.php

See merge request ispconfig/ispconfig3!709

Update cron.sh

See merge request ispconfig/ispconfig3!711

Support mail filtering by envelope :detail (+ part in mail addresses)

See merge request ispconfig/ispconfig3!703

Improvements in using HTTP2 and talking about version

See merge request ispconfig/ispconfig3!705

Fix for #4335 and removal of unnecessary file

See merge request ispconfig/ispconfig3!706

Improvements

See merge request freeos/ispconfig3!1

Stable 3.1

See merge request ispconfig/ispconfig3!704