add action for posting staff

module/schools/src/Action/StaffCreate.php

+<?php
+/**
+ * gredu_labs.
+ *
+ * @link https://github.com/eellak/gredu_labs for the canonical source repository
+ *
+ * @copyright Copyright (c) 2008-2015 Greek Free/Open Source Software Society (https://gfoss.ellak.gr/)
+ * @license GNU GPLv3 http://www.gnu.org/licenses/gpl-3.0-standalone.html
+ */
+
+namespace GrEduLabs\Schools\Action;
+
+use Slim\Http\Request;
+use Slim\Http\Response;
+
+class StaffCreate
+{
+
+    public function __construct($staffservice)
+    {
+        $this->staffservice = $staffservice;
+    }
+
+    public function __invoke(Request $req, Response $res, array $args = [])
+    {
+        $staff = $this->staffservice->getTeacherById(1);
+        $res = $res->withJson($staff->export());
+        return $res;
+    }
+}