Check for event type conference on the submit-event page

Hello everyone, Even though we clearly state that "conference submissions should be emailed to php-webmaster@lists.php.net" there are still a couple of conferences making their way into the events. I would propose adding an event type "Conference" to the drop down and trigger an error on submission for that event type, to avoid the case where people do not read the first paragraph. What do you think? Best, Stelian