Add support dumping and loading from JSON/YAML in gaudirun.py

this MR adds the possibility of dumping a configuration as .json and .yaml via the gaudirun.py --output option (same as with .opts, .pkl and .py formats).

The generated JSON/YAML files can then be used as input to the configuration, same as .opts or .pkl files (.py dumps cannot be used to configure the application).

The support for .yaml (or .yml) dumps is available only if the Python package PyYAML is available.

Closes #200 (closed)