Add service definition for DateTimeFormatter (related to #3632)

[localheinz]

When attempting to add a DateTimeFormatter filter to the filter chain of an input like this

$this->add(array(
    'name' => 'release_date',
    'filters' => array(
        array(
            'name'  => 'DateTimeFormatter',
        ),
    ),
));

a ServiceNotFoundException is thrown because the FilterPluginManager is unaware of a factory.

[localheinz]

Ping @davidwindell.

[davidwindell]

👍