Refactory Writer Styles to match new code organization (#433)

Decomposed old StyleHelper into StyleManager, StyleRegistry and StyleMerger.

tests/Spout/Writer/Common/Manager/Style/StyleManagerTest.php

@@ -0,0 +1,52 @@
+<?php
+
+namespace Box\Spout\Writer\Common\Manager\Style;
+
+use Box\Spout\Writer\Common\Creator\Style\StyleBuilder;
+
+/**
+ * Class StyleManagerTest
+ *
+ * @package Box\Spout\Writer\Common\Manager\Style
+ */
+class StyleManagerTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @return StyleManager
+     */
+    private function getStyleManager()
+    {
+        $style = (new StyleBuilder())->build();
+        $styleRegistry = new StyleRegistry($style);
+
+        return new StyleManager($styleRegistry);
+    }
+
+    /**
+     * @return void
+     */
+    public function testApplyExtraStylesIfNeededShouldApplyWrapTextIfCellContainsNewLine()
+    {
+        $style = (new StyleBuilder())->build();
+        $this->assertFalse($style->shouldWrapText());
+
+        $styleManager = $this->getStyleManager();
+        $updatedStyle = $styleManager->applyExtraStylesIfNeeded($style, [12, 'single line', "multi\nlines", null]);
+
+        $this->assertTrue($updatedStyle->shouldWrapText());
+    }
+
+    /**
+     * @return void
+     */
+    public function testApplyExtraStylesIfNeededShouldDoNothingIfWrapTextAlreadyApplied()
+    {
+        $style = (new StyleBuilder())->setShouldWrapText()->build();
+        $this->assertTrue($style->shouldWrapText());
+
+        $styleManager = $this->getStyleManager();
+        $updatedStyle = $styleManager->applyExtraStylesIfNeeded($style, ["multi\nlines"]);
+
+        $this->assertTrue($updatedStyle->shouldWrapText());
+    }
+}