Move it, adding a date based suffix. A cronjob should purge or archive.

This reverts merge request !1076

In addition to /conf-custom/mail/welcome_email_DOMAINNAME.txt and /conf-custom/mail/welcome_email_LANGUAGE.txt one may place a /conf-custom/mail/welcome_email_DOMAINNAME.html or /conf-custom/mail/welcome_email_LANGUAGE.html file to allow HTML based welcome messages.

* In addition to language specific custom welcome messages (when creating a new mail account) this patch will
allow to have a welcome message template for each domain.

* To add a domain specific welcome message, place a file at /usr/local/ispconfig/server/conf-custom/mail/
and name it according the domain, like welcome_email_example.com.txt

* i.e. /usr/local/ispconfig/server/conf-custom/mail/welcome_email_example.com.txt

will be used if a mailbox for example.com is created.

Added prefetching to dovecot to halve database-queries
Added mdbox-creation for new Mailboxes in mdbox-format

Conflicts:
	install/tpl/debian6_dovecot-sql.conf.master
	install/tpl/debian_dovecot-sql.conf.master
	install/tpl/debian_postfix.conf.master
	install/tpl/fedora_dovecot-sql.conf.master
	install/tpl/fedora_postfix.conf.master
	install/tpl/gentoo_postfix.conf.master
	install/tpl/opensuse_dovecot-sql.conf.master
	install/tpl/opensuse_postfix.conf.master
	interface/web/admin/templates/server_config_mail_edit.htm
	server/cron_daily.php
	server/plugins-available/mail_plugin.inc.php
	server/plugins-available/postfix_server_plugin.inc.php

do not change parameter order in old functions

do not change parameter order in old functions

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Feature can be activated over admin mailserver settings. when activated websites uid is used instead of standard vmail-uid. this only takes effect if web and mailserver are on the same server, otherwise it will be old behaviour. switching this setting when mailboxes exist doesn't matter. Mailboxfolder will be created with website uid for this. access of postfix and dovecot now works over mysql-table mail_user. virtual_uid_maps is changed from static to mysql-table. for dovecot<->postfix communication protocoll is changed vrom lda to lmtp. disablelmtp-column is added to mail_user-table. uid and gid can be overwritten by remoting.
ONE OPEN ISSUE: since remoting has completly changed and mail_user_add function is missing at the moment, this function now was inclulded again. it is important to add the both new lines to the future function and then remove this new one.