fix multi net-volume & for override inherited class ＆ net-unmount & cmd: url

Net volume is a wonderful function. 
How is this proposal? 

ex. I use next inherited class

<pre>
require_once _MD_ELFINDER_LIB_PATH . '/php/elFinderVolumeFTP.class.php';

elFinder::$netDrivers['ftp'] = 'FTPx';

class elFinderVolumeFTPx extends elFinderVolumeFTP {
	protected function configure() {
		$this->tmbPath = XOOPS_ROOT_PATH .
'/modules/'._MD_ELFINDER_MYDIRNAME.'/cache';
		
		parent::configure();

		$this->disabled[] = 'pixlr';
	}
}
</pre>

and ...

Add command "netunmount"

and ...

Add command "url" (Get permalink url. For network volume that needs to create a permalink.)