Consolidate external EntityFactory

All entities will now be created through a single factory (including the Writers).
Also, added a EntityFactory::createRowFromArray() to make it easier to create rows

tests/Spout/Writer/Common/Creator/WriterFactoryTest.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace Box\Spout\Writer\Common\Creator;
+
+use Box\Spout\Common\Exception\UnsupportedTypeException;
+
+/**
+ * Class WriterFactoryTest
+ */
+class WriterFactoryTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @return void
+     */
+    public function testCreateWriterShouldThrowWithUnsupportedType()
+    {
+        $this->expectException(UnsupportedTypeException::class);
+
+        (new WriterFactory())->create('unsupportedType');
+    }
+}