My proposed version for `feature/response-exception`

Here another proposal for `feature/response-exception`, which adds the following:

- Additional security by applying `basename()` to the template name
- Return relative paths in `getTemplateFile()`
- Remove the potentially insecure changes regarding a variable template path

Correct. E.g.

```php
throw new TemplateResponseException(
    'vendor/contao/module-core/src/templates/backend/be_referer.html5',
    200,
    [],
    'Invalid request token. Please <a href="javascript:window.location.href=window.location.href">go back</a> and try again.'
);
```