Update config loading code
Combining two cookiecuttor-toolforge commits [1][2].
[1]: https://github.com/lucaswerkmeister/cookiecutter-toolforge/commit/6efec9b6a08e2278279d11d2fd6bc9de13159e33
[2]: https://github.com/lucaswerkmeister/cookiecutter-toolforge/commit/17ef149635e37676c944486c49d2f9a2cd46ef6f