rewrite export controller and manager

- upgrade to symfony 4 ;
- add support for directExportInterface

Export/DirectExportInterface.php

@@ -0,0 +1,15 @@
+<?php
+/*
+ * 
+ */
+namespace Chill\MainBundle\Export;
+
+use Symfony\Component\HttpFoundation\Response;
+
+/**
+ * 
+ */
+interface DirectExportInterface extends ExportElementInterface
+{
+    //put your code here
+}