function addButton($name, $callback, $admin = false, $pluginId = null)
	{
		if(!isset($this->menu[$pluginId]))
			$this->initMenu(Icons128x128_1::DefaultIcon, $pluginId);
		
		$this->menu[$pluginId]['buttons'][] = array('name' => $name, 'callback' => $callback, 'admin' => $admin);
		
		if($this->loaded)
			$this->refreshMenubar();
	}