improved code styles #158 (#172)

* use php-cs-fixer instead of phpcodesniffer
* updated scrutinizer config
* adjusted code yules to all files
* updated CONTRIBUTING guidelines

tests/Controller/InvoiceControllerTest.php

@@ -17,7 +17,6 @@ use App\Entity\User;
  */
 class InvoiceControllerTest extends ControllerBaseTest
 {
-
     public function testIsSecure()
     {
         $this->assertUrlIsSecured('/invoice/');