Move plugin files to a subfolder

[MAILPOET-3988]

mailpoet/lib/Models/MappingToExternalEntities.php

@@ -0,0 +1,13 @@
+<?php
+
+namespace MailPoet\Models;
+
+class MappingToExternalEntities extends Model {
+  public static $_table = MP_MAPPING_TO_EXTERNAL_ENTITIES_TABLE; // phpcs:ignore PSR2.Classes.PropertyDeclaration
+
+  public static function create($data = []) {
+    $relation = parent::create();
+    $relation->hydrate($data);
+    return $relation->save();
+  }
+}