[core/config] Add support for configuration files
[core/config] Add support for configuration files

Load configuration files from a number of places and, if they exist, use
the settings there as baseline settings that can be overwritten by more
specific source (the modules themselves and the CLI `--parameter`
option).

TODO: document this

tobi-wan-kenobi/bumblebee-status,tobi-wan-kenobi/bumblebee-status