Tests
Added 'addOption' to OptionsManagerInterface
Moved 'setColumnWidths' and 'mergeCells' methods to Xlsx Writer implementation since the actual feature only works for Xlsx at the moment
shrinkToFit was not handled in StyleMerger so it was overwritten by the default cell style
StyleManager didn't add the property to the xml if shrinkToFit was used without alignment or text wrap.
Unit test
István Ignácz