Add Entity for default_queue table

I think it would be nice to have entity beside the SQL file, so that we can use this in combination with "orm:schema-tool:update" instead of manually importing SQL. Please review.
@tad3j [type hinting](http://php.net/manual/en/language.oop5.typehinting.php) is "to force parameters to be objects [...], interfaces, arrays [...] or callable [...]".

You go from this:

    public function setCreated($created)

To this:

    use DateTime;
    public function setCreated(DateTime $created)

It makes sure `$created` is an instance of `DateTime` for this method, ensuring nothing other could be passed onto this method.