Added autoresponder function and custom maildrop rules.

install/install.php

install/lib/installer_base.lib.php

install/tpl/mailfilter.master

interface/lib/classes/tform.inc.php

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

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

interface/web/mail/templates/mail_user_mailfilter_edit.htm

server/conf/autoresponder.master

server/lib/classes/modules.inc.php

server/plugins-enabled/maildrop_plugin.inc.php