Added more tests (#965)

Improved testing ...

After the initializer scripts were removed, we didn't test the actual compose setup anymore. This adds new tests to run the database migrations.

Initializers are now a plugin

Changed entrypoint to "tini".

Format shell scripts with shfmt

NetBox should always be referred to as NetBox ...

Fix all instances of "Netbox".

```Shell
git ls-files -z . | xargs --null -I '{}' find './{}' -type f -print0 | xargs --null sed --in-place --regexp-extended 's#Netbox#NetBox#g;'
```

Ref: https://netbox.readthedocs.io/en/stable/development/style-guide/#branding

Skip Startup Scripts in Unit Tests

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.

Fix leftover from testing in test.sh

Simplify test script for manual tests

Merge pull request #222 from netbox-community/fix-github-action ...

Fix Github Action

Re-enable Netbox unit tests

Fix failing GH Action

Improve test.sh ...

Don't move the original initializers directory, but rather use the one
with the modified initializers in it.

Building the Docker image with Github Actions

Adds a test that validates the initializer yml files