Add service definition for DateTimeFormatter (related to #3632)

When attempting to add a `DateTimeFormatter` filter to the filter chain of an input like this

```php
$this->add(array(
    'name' => 'release_date',
    'filters' => array(
        array(
            'name'  => 'DateTimeFormatter',
        ),
    ),
));
```

a `ServiceNotFoundException` is thrown because the `FilterPluginManager` is unaware of a factory.