[NFR] Validation messages code

[viktoras25]

Currently messages (e.g. model messages) support only 3 parameters: field, text and type. I, however, find that code parameter is also important (as for me much more important than type). Message text may differ over time, if you want to reformulate it, or fix some typo, message code at the same time should stay always the same. It is unique identifier of an error in the system. Think of an exception, they do have type, message text and code.

Please, implement codes for messages. It would be also very nice if validators would accept a code as an option, to pass to a message.

It doesn't seem to be an unnecessary complication.

Thanks in advance.

Proposed changes:

$message = new Message($message, $field, $type, $code) {...}
$message->setCode(103);
$message->getCode(); // int(103)

// model.php
$this->validate(new PresenceOf(array(
    "message" => "Field required",
    "code" => 103
)));