Freeze pane should use xsplit/ysplit instead of topLeftCell

[adriencohen]

This is:

• a bug report
• a feature request
• not a usage question (ask them on https://stackoverflow.com/questions/tagged/phpspreadsheet or https://gitter.im/PHPOffice/PhpSpreadsheet)

What is the expected behavior?

The freezed pane should be the same after loading and saving an xlsx file

What is the current behavior?

The freezed pane changes of place.

For example if I have a xlsx with this
<pane xSplit="5" ySplit="11" topLeftCell="GG646" activePane="bottomRight" state="frozen"/>
It displays this in Excel and LibreOffice

topLeftCell defines the bottom right pane to show but not the "frozen" part, we need to use xsplit/ysplit to define the frozen part. The current version uses topLeftCell, so with topLeftCell="GG646" you will not be able to navigate in your spreassheet because most rows/columns are frozen.

What are the steps to reproduce?

I don't think that this bug can't be reproduce without an example file.
By executing this script you will see that the frozen pane (top left one) will move.
strange.xlsx

<?php


$reader = new \PhpOffice\PhpSpreadsheet\Reader\Xlsx();
$spreadsheet = $reader->load('strange.xlsx');
$writer = new \PhpOffice\PhpSpreadsheet\Reader\Xlsx($spreadsheet);
$writer->save("out.xls");

Which versions of PhpSpreadsheet and PHP are affected?

PhpSpreadsheet : 1.0.0-beta
php -v
PHP 7.1.2 (cli) (built: Feb 23 2017 19:07:37) ( NTS )
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