Added support for wildcards in the ExifMetadata listener

This PR adds support for wildcards when configuring which tags to insert as metadata for new images.

```php
return array(
    'eventListeners' => array(
        'exifMetadataListener' => array(
            'listener' => 'Imbo\EventListener\ExifMetadata',
            'params' => array(
                array('exif:*', 'date:*', 'png:gAMA'),
            ),
        ),
    ),
);
```

The above configuration will insert all `exif` and `date` tags, along with `png:gAMA`. The default value is `exif:*`. The PR also adds extra tests for the event listener.