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

Ok, and how will it work if people currently used `die_nicely` in their extension? Can we assume that was never the case (because it would only work with core template)? Then we could also simply drop `die_nicely`