incomplete configuration structure

[Rykath]

PR #142 introduced a new configuration structure using classes, but in practice the objects are converted to dictionaries in the end.
A reevaluation of the new structure might also reveal further room for improvement.

Incomplete:

• accessing the configuration is done mostly using config['key'] and not config.key
• config.variables contains a dictionary generated from Variables and not the objects themselves (in main the objects are used again)
• the new classes use to_dict (or similar) instead of implementing the necessary methods for a MutableMapping (see docs, especially .items())

Possible improvements (time will tell):

• central defaults file vs defaults near the implementation
• a system default.yaml file which is read before profit.yaml
• config classes in a central file vs near the implementation