[VolumeDriver] add options['plugin'] & method getOptionsPlugin($name)
[plugin:Watermark] support volume driver option "plugin"

# Connector configuration options

$opts = array(
    'roots'  => array(
         array(
            'driver' => 'LocalFileSystem',
            'path'   => '/path/to/files/',
            'URL'    => 'http://localhost/to/files/',
            'plugin' => array(
                /* optional, this volume values are */
                'Watermark' => array(
                    'enable'         => true,       // For control by volume driver
                    'source'         => 'logo.png', // Path to Water mark image
                    'marginRight'    => 5,          // Margin right pixel
                    'marginBottom'   => 5,          // Margin bottom pixel
                    'quality'        => 90,         // JPEG image save quality
                    'transparency'   => 90, // Water mark image transparency
                                            // ( other than PNG )
                    'targetType'     => IMG_GIF|IMG_JPG|IMG_PNG|IMG_WBMP,
                                        // Target image formats ( bit-field )
                    'targetMinPixel' => 200         // Target image minimum 
                                                    // pixel size
                ),
            ),
    ),
    'bind'   => array(
        /* regist action, require */
        'upload.presave' => 'Plugin.Watermark.onUpLoadPreSave',
    ),
    'plugin' => array(
        /* optional, All volume's default values are */
        'Watermark' => array(
            'enable'         => true,       // For control by volume driver
            'source'         => 'logo.png', // Path to Water mark image
            'marginRight'    => 5,          // Margin right pixel
            'marginBottom'   => 5,          // Margin bottom pixel
            'quality'        => 90,         // JPEG image save quality
            'transparency'   => 90, // Water mark image transparency
                                    // ( other than PNG )
            'targetType'     => IMG_GIF|IMG_JPG|IMG_PNG|IMG_WBMP,
                                // Target image formats ( bit-field )
            'targetMinPixel' => 200         // Target image minimum 
                                            // pixel size
        ),
    ),
);
$connector = new elFinderConnector(new xelFinder($opts), true);
$connector->run();