replaced closure by callbacks

lib/Config/Hooks.php

@@ -116,21 +116,32 @@ class Hooks {
   }
 
   function setupImageSize() {
-    add_filter('image_size_names_choose', function($sizes) {
+    add_filter(
+      'image_size_names_choose',
+      array($this, 'appendImageSize'),
+      10, 1
+    );
+  }
+
+  function appendImageSize($sizes) {
     return array_merge($sizes, array(
       'mailpoet_newsletter_max' => __('MailPoet Newsletter')
     ));
-    });
   }
 
   function setupListing() {
-    // handle saving "per_page" screen option
+    add_filter(
-    add_filter('set-screen-option', function($status, $option, $value) {
+      'set-screen-option',
+      array($this, 'setScreenOption'),
+      10, 3
+    );
+  }
+
+  function setScreenOption($status, $option, $value) {
     if(preg_match('/^mailpoet_(.*)_per_page$/', $option)) {
       return $value;
     } else {
       return $status;
     }
-    }, 10, 3);
   }
 }