If no path is given in the environment variable CORE_CONFIGFILE, different
standard locations will be probed:
- os.UserConfigDir() + /datarhei-core/config.js
- os.UserHomeDir() + /.config/datarhei-core/config.js
- ./config/config.js
If the config.js doesn't exist in any of these locations, it will be
assumed at ./config/config.js