update config handling:

[gernotstarke]

the MVP skipped several config items (header, footer, chapter-ids) for sake of faster speed-to-market.

Those should be added now.

The former config package should be (re-)included in the internal packages.

[gernotstarke]

will add issues for every required flag/flag+param combo

[gernotstarke]

still not good enough: I want a layered configuration: cli parameters -> (overwrites) config file -> defaults.

Therefore we add more sophisticated frameworks (e.g. viper) to handle such configuration.