Merge branch 'ispconfig/ispconfig3-stable-3.1' into stable-3.1

install/dist/lib/fedora.lib.php

install/dist/lib/gentoo.lib.php

install/dist/lib/opensuse.lib.php

install/lib/installer_base.lib.php

interface/lib/classes/validate_domain.inc.php

interface/web/sites/form/web_vhost_domain.tform.php

interface/web/sites/lib/lang/ar_web_domain.lng

interface/web/sites/lib/lang/bg_web_domain.lng

interface/web/sites/lib/lang/br_web_domain.lng

interface/web/sites/lib/lang/ca_web_domain.lng

interface/web/sites/lib/lang/cz_web_domain.lng

interface/web/sites/lib/lang/de_web_domain.lng

interface/web/sites/lib/lang/dk_web_domain.lng

interface/web/sites/lib/lang/el_web_domain.lng

interface/web/sites/lib/lang/en_web_domain.lng

interface/web/sites/lib/lang/es_web_domain.lng

interface/web/sites/lib/lang/fi_web_domain.lng

interface/web/sites/lib/lang/fr_web_domain.lng

interface/web/sites/lib/lang/hr_web_domain.lng

interface/web/sites/lib/lang/hu_web_domain.lng