We replace the current environment variable based configuration approach by
reading all local configuration from a `settings.toml` configuration file.
The docker test, development and production setups have been updated to use
the new setup.
The configuration folder also allows overriding every template in a
`config/templates` directory. We use this in a follow-up to move
all local specific templates, e.g. the registration form, into this
config directory.
Christian Merten