Don't load main config twice ...

Before, the main_config (e.g. 'configuration.py' or 'ldap_config.py') were loaded twice.
The first load was hard-coded and correct.
The second load was during the discovery phase for dynamic configurations.
This has now been fixed. During the discovery for dynamic configurations,
the main_config file is now excluded.

Thanks @tobiasge for discovering this bug.

Use black as formatter for python files

Gunicorn is replaced with nginx-unit ...

We now serve Netbox with an nginx-unit instance instead of Gunicorn.
This allows us to get rid of the extra Nginx container because Unit is
also serving the static files. The static files are now collected at container
buildtime instead of every startup.

Merge core functionality into `configuration.py` ...

Which is the file `docker/configuration.docker.py` in our repo.
The common code is then imported by `docker/ldap_config.docker.py`.

Revert accidential change to _read_secret order

Consistency in namespace name

Dot character has special meaning in module names ...

Therefore we esacpe it using the underscore character.

Dynamically load configuration files

Move config to /etc/netbox/config (Fixes #54) ...

With this the configuration is moved to /etc/netbox/config and the
default reports directory is set to /etc/netbox/reports. This enables
the user to mount reports from a config map or persistent volume in
OpenShift.

Modifications for Openshift ...

With these modifications the netbox containers can run on Openshift.
The configuration files can be imported from a config map to the
'/etc/netbox' directory and will be loaded from there.

🐞 Convert numbers from ENV to int ...

Fixes #36

❇️ Make the default configuration cluster ready ...

This changes the default configuration to be better prepared for
usage with container management platforms, such as Docker Swarm,
Kubernetes or OpenShift.

Closes #27.

Allow setting ENFORCE_GLOBAL_UNIQUE in env

🐞 The upstream repo remove the docker config ...

.. so I copied it over to this repo.