When freeze pane is in use on a worksheet, PhpSpreadsheet saves to Xlsx in such
a way that the active cell is always set to the top left cell below the freeze
pane. I find it difficult to understand why:
1. You have given users the setSelectedCells function, but then choose to
ignore it.
2. Excel itself does not act in this manner.
3. PHPExcel did not act in this manner.
4. PhpSpreadsheet when writing to Xls does not act in this manner.
This is especially emphasized because the one test in FreezePaneTest which
would expose the difference is the only test in that member which is
not made for both Xls and Xlsx.
5. It is *really* useful to be able to open a spreadsheet anywhere, even when
it has header rows.
Closes#1323
Properly set the selected cells for worksheets with frozen panes when
writing Xlsx documents. Beforehand, the saved Xlsx documents were
generating corruption warnings when opened in Excel.
Fixes#532Closes#535
Adrien Crivelli