- Renames router URL query parameter and router class

- Updates other classes to use the new name
- Updates unit tests

tests/unit/Router/RouterTestMockEndpoint.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace MailPoet\Router\Endpoints;
+
+class MockEndpoint {
+  const ACTION_TEST = 'test';
+  public $allowed_actions = array(
+    self::ACTION_TEST
+  );
+  public $data;
+
+  function __construct($data) {
+    $this->data = $data;
+  }
+
+  function test() {
+    return $this->data;
+  }
+}