Added another dynamic row_option to provide row collapse functionality.

[ThornyS]

Hi,
I find this xlsx package great!! and Thank You.
I had noticed that as part of the writeSheetRow function the $row_options has become partially dynamic.
I needed to also make the outlineLevel dynamic to apply a multi-row collapse effect.
I've added an examples file ex11-row-group-collapse.php to show it working.
e.g.
$row_options = array('collapse' => true, 'hidden' => true, 'outlineLevel' => 1);
$writer->writeSheetRow('Sheet1', $row_data, $row_options);