Magento Adminhtml Produkt bearbeitung Button hinzufügen (add button on product edit page)

<?xml version="1.0"?>
<config>
    <modules>
        <M28visions_AddAdminhtmlOptionsButton>
            <version>0.0.1</version>
        </M28visions_AddAdminhtmlOptionsButton>
    </modules>
    <frontend>
    </frontend>
    <global>
        <blocks>
            <m28visions_addadminhtmloptionsbutton>
                <class>M28visions_AddAdminhtmlOptionsButton_Block</class>
            </m28visions_addadminhtmloptionsbutton>
            <adminhtml>
                <rewrite>
                    <catalog_product_edit>M28visions_AddAdminhtmlOptionsButton_Block_Adminhtml_Catalog_Product_Edit</catalog_product_edit>
                </rewrite>
            </adminhtml>
        </blocks>
    </global>
</config>

<?php
 
class M28visions_AddAdminhtmlOptionsButton_Block_Adminhtml_Catalog_Product_Edit extends Mage_Adminhtml_Block_Catalog_Product_Edit
{
    /**
     * @var Mage_Catalog_Model_Product Product instance
     */
    private $_product;
 
    /**
     * Preparing global layout
     * 
     * @return M28visions_AddAdminhtmlOptionsButton_Block_Adminhtml_Catalog_Product_Edit|Mage_Core_Block_Abstract
     */
    protected function _prepareLayout()
    {
        parent::_prepareLayout();
        $this->_product = $this->getProduct();
        $this->setChild('view_on_front',
            $this->getLayout()->createBlock('adminhtml/widget_button')
                ->setData(array(
                'label'     => Mage::helper('catalog')->__('Add Product Options'),
                'onclick'   => 'setLocation(\''.$this->getUrl('m28adminhtml/adminhtml_product', array('_current'=>true)).'\')',
                'disabled'  => !$this->_isVisible(),
                'title'     => Mage::helper('catalog')->__('Add Product Options')
            ))
        );
 
        return $this;
    }
 
    /**
     * Returns duplicate & view on front buttons html
     * 
     * @return string
     */
    public function getDuplicateButtonHtml()
    {
        return $this->getChildHtml('duplicate_button') . $this->getChildHtml('view_on_front');
    }
 
    /**
     * Checking product visibility
     * 
     * @return bool
     */
    private function _isVisible()
    {
        return $this->_product->isVisibleInCatalog() && $this->_product->isVisibleInSiteVisibility();
    }
 
}

<?xml version="1.0"?>
<config>
    <modules>
        <M28visions_AddAdminhtmlOptionsButton>
            <active>true</active>
            <codePool>local</codePool>
        </M28visions_AddAdminhtmlOptionsButton>
    </modules>
</config>