Convert aggregator_feed_add to a new style controller

+++ b/core/modules/aggregator/lib/Drupal/aggregator/Routing/AggregatorController.phpundefined
@@ -0,0 +1,59 @@
+  /**
+   * Stores the Entity manager.
+   *
+   * @var \Drupal\Core\Entity\EntityManager
+   */
+  protected $entityManager;

Talked with paris whether it makes sense to store the storage controller instead, but on the longrun more page callbacks will be converted, so they will need the entity manager again.

Committed 04fd884 and pushed to 8.x. Thanks!