fixup! Lint the syntax of changes

Lint the syntax of changes

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

Update actions/checkout action to v2

Prevent "alpine:edge" from failling the workflow ...

Alpine is releases a new version once a year. Therefore our workflow
runs don't need to be marked as failed when run on alpine:edge

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.

Disable tests for Python 3.10-rc ...

Some of the dependencies of Netbox can't be built with Python 3.10.

Upgrade Python image to 3.9-alpine ...

Upgrade the default base image to Python 3.9 and start testing on Python 3.10-rc

Use release version of Python 3.9 in tests

Enable test on Python 3.9

Move default source image to Python 3.8

Changed "build-branches.sh" to "build-next.sh" ...

The old version of "build-branches.sh" skipped the pushing of images when one of
them didn't change its sources. When looking at the Netbox branches I noticed
that the "master" branch only changes when there is a new release. Because we
build the new releases anyway in "build-latest.sh" that leaves "develop" and
"develop-*" which change regularly. The new script "build-next.sh" is responsible
for building "develop-*" as the next major release of Netbox. The build of
"develop" is moved to the Github Action build matrix. This has the additional
advantage of being faster because more builds are done in parallel.

Enable push workflow for PRs

Merge pull request #229 from netbox-community/fix_shields ...

Readme Cleanup

Disable python 3.9 tests once more

Fix build status badge

Fix failing GH Action

Enable tests with Python 3.9

Netbox is not yet compatible with Python 3.9

Building the Docker image with Github Actions