I reviewed character escaping everywhere with the following ideas:
* use a single common function to escape user data: `escape` using `htmlspecialchars`.
* sanitize fields in `index.php` after reading them from datastore and before sending them to templates.
It means no escaping function in Twig templates.
2 reasons:
* it reduces risks of security issue for future user made templates
* more readable templates
* sanitize user configuration fields after loading them.
