ODS writer

Added ODS writer
Refactored XLSX writer to abstract some pieces into an abstract multi-sheets writer
Created an abstract style helper
Moved shared components around

src/Spout/Reader/XLSX/RowIterator.php

@@ -77,6 +77,7 @@ class RowIterator implements IteratorInterface
         $this->sharedStringsHelper = $sharedStringsHelper;
 
         $this->xmlReader = new XMLReader();
+        /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
         $this->escaper = new \Box\Spout\Common\Escaper\XLSX();
     }