CraftsPage.php

<?php
class CraftsPage extends Page {

	static $has_many = array(
		'Files' => 'ImageAndFile'
	);

	public function getCMSFields() {
		$fields = parent::getCMSFields();

		foreach (array('Files') as $field) {
			$config = new GridFieldConfig_RelationEditor();
			$config->addComponent(new GridFieldSortableRows('SortOrder'));
			$config->addComponent($uploader = new GridFieldBulkUpload());
			$uploader->setUfSetup('setFolderName', 'Uploads/Craft/Images');
			$config->addComponent(new GridFieldBulkManager());
			$config->addComponent(new GridFieldGalleryTheme('Image'));
			$fields->addFieldToTab('Root.' . $field, new GridField($field, null, $this->{$field}(), $config));
		}
		return $fields;
	}

}


class CraftsPage_Controller extends Page_Controller {

	
}

ImageAndFile.php

<?php

/**
 * Class Partner
 *
 * @property String $Title
 * @property Int    $SortOrder
 * @method Image Image()
 * @method File File()
 */
class ImageAndFile extends DataObject {

	private static $db = array(
		'Title'     => 'Varchar',
		'SortOrder' => 'Int'
	);

	public static $default_sort = 'SortOrder';

	private static $has_one = array(
		'Image' => 'Image',
		'File'  => 'File',
		'Page'  => 'Page'
	);

	private static $summary_fields = array(
		'Title',
		'File.Title'
	);

	public function getCMSFields() {
		$fields = parent::getCMSFields();

		/** @var Upload_Validator $validator */
		$validator = $fields->fieldByName('Root.Main.Image')->getValidator();
		$validator->setAllowedExtensions(array('jpg', 'png'));

		$fields->removeFieldFromTab('Root.Main', 'SortOrder');

		return $fields;
	}
}