Database: Use foreign keys
I stumbled across a bunch a DB->delete() statements (https://dev.quiqqer.com/sequry/core/blob/dev/src/Sequry/Core/Password.php#L842). To clear up the code and preventing developers from forgetting to add/remove tables here, when updating the database scheme, foreign keys could/should be used.
When doing this - in the example above - a simple delete (with cascade) on the main password table would be enough to remove entries for this password from all tables.