List selection & subscribe

- fixed list selection widget (form editor & rendered form)
- ajax subscription works (minus sending the confirmation email)
- bug fixes / polishing / refactoring / cleanup

lib/Listing/ItemAction.php

@@ -1,36 +0,0 @@
-<?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)
-      );
-    }
-  }
-}