Added postfix header- and body check filters.

install/lib/installer_base.lib.php

install/sql/ispconfig3.sql

install/tpl/config.inc.php.master

interface/lib/config.inc.php

interface/web/mail/form/mail_content_filter.tform.php

interface/web/mail/lib/lang/en_mail_content_filter.lng

interface/web/mail/lib/lang/en_mail_content_filter_list.lng

interface/web/mail/lib/module.conf.php

interface/web/mail/list/mail_content_filter.list.php

interface/web/mail/mail_content_filter_del.php

interface/web/mail/mail_content_filter_edit.php

interface/web/mail/mail_content_filter_list.php

interface/web/mail/templates/mail_content_filter_edit.htm

interface/web/mail/templates/mail_content_filter_list.htm

server/mods-enabled/mail_module.inc.php