Generate internal filenames based on attachment name.

The filename of the uploaded file is now safed in the database.

src/Entity/Attachments/Attachment.php

@@ -237,6 +237,7 @@ abstract class Attachment extends NamedDBElement
     public function setFilename(?string $new_filename): Attachment
     {
         $this->original_filename = $new_filename;
+        return $this;
     }
 
     /**