Hierarchy of configuration files

[rettigl]

We have been discussing to allow for several levels of configuration files, that are automatically searched for and included, and take preference in a certain hierarchy:

• at top level, a configuration file stored together with an analysis script should be considered. This can be e.g. used to store calibration parameters for a given dataset, and also data-dependent metadata.
• There should be a user-defined configuration file. This could be placed in the user document folder (e.g. ~user/.sed/).
• We could also think about a site-specific config. Not sure what is the best way to define this, and/or if the user-config is sufficient
• last, there should be a package default

[rettigl]

Closed by PR #111