Major refactoring of listing/router/model relation

- updated Subscribers listing
- udpated Segments listing
- added Forms router

lib/Listing/ItemAction.php

@@ -0,0 +1,36 @@
+<?php
+namespace MailPoet\Listing;
+
+if(!defined('ABSPATH')) exit;
+
+class ItemAction {
+  private $model = null;
+  private $action = null;
+  private $data = null;
+
+  function __construct($model_class, $data) {
+    $id = (int)$data['id'];
+    unset($data['id']);
+    $this->action = $data['action'];
+    unset($data['action']);
+    $this->model = $model_class::findOne($id);
+    if(!empty($data)) {
+      $this->data = $data;
+    }
+    return $this;
+  }
+
+  function apply() {
+    if($this->data === null) {
+      return call_user_func_array(
+        array($this->model, $this->action),
+        array()
+      );
+    } else {
+      return call_user_func_array(
+        array($this->model, $this->action),
+        array($this->data)
+      );
+    }
+  }
+}