🐞 REDIS_PORT should be int ...

Closes #96

♻️ Make netbox-worker it's own container ...

One container should ideally have one responsibility [1]. Therefore I
implemented the netbox-worker to start in it's own container. This is
possible, because netbox and the worker communicate via redis anyway.

They still use the same image underneath, just the "command" they
execute while starting different.

Or in other words: I see no reason to introduce supervisord, when we
already have docker-compose which can take care of running multiple
processes.

Also, here's another benefit: Now it's possible to view the logs of the
webhook worker independently of the other netbox logs (and vice-versa).

Other changes in this commit:
* I don't see a reason to put a password for Redis in the docker-compose
  setup, so I removed it.
* Slightly changed the nginx config, so that the nginx startup command
  becomes simpler and any error should be visible in the docker log.
* Some housekeeping in the `Dockerfile`.
* Added some troubleshooting advice regarding webhooks to the README.

I'd like to thank Brady (@bdlamprecht [2]) here who did the harder
work of figuring out what's even required to have webhooks working. [3]

[1] 
https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#decouple-applications
[2] https://github.com/bdlamprecht
[3] https://github.com/ninech/netbox-docker/pull/90

✨ Disable webhooks by default* ...

*but enable it by default for anyone who checks out the netbox-docker project
via the netbox.env file.

✨ Read redis password like any other secret

Working implementation of webhooks using new 'redis' container

Merge branch 'master' into master

Update ldap_config.py

Change default value of AUTH_LDAP_USER_DN_TEMPLATE

Add auth-ldap-user-dn-template in ldap_config.py

resolve AUTH_LDAP_GROUP_CACHE_TIMEOUT from env ...

Resolve ValueError: invalid literal for int() for AUTH_LDAP_GROUP_CACHE_TIMEOUT

add allow all hosts by default

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.

🐞 Parse config correctly ...

Fixes #56

Externalize gunicorn-config ...

This moves the gunicorn_config.py into /etc/netbox so that it can be
easily mapped through a Openshift config map

Add django_ldap_auth ...

In the ldap.Dockerfile the django_ldap_auth module is installed to
enable authentication againt LDAP servers.

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.