## Description
Replace Caddy with Traefik
## Rationale
There is some trouble with the Caddy license (https://github.com/pydanny/cookiecutter-django/pull/1282#issuecomment-329617536)
@drdaeman suggested using Traefik (https://github.com/pydanny/cookiecutter-django/pull/1282#issuecomment-353655273) which supports ACME and also plays very nice with Docker.
## Comments
I am currently using the proposed setup on a live site and it working great so far. If this PR is of interest to the maintainers, then I could commit more changes and take care of the documentation. Of course, any suggestions by the more experienced people around here, are welcome!
* Create a test matrix on Travis CI to help testing multiple options
* Change test_docker.sh to fail if any command in it fails
* Run black on the CI with --check option
* Fix formatting of project files using black
* Install black in the docker container
* Exclude migrations in black checks
* Fix Black formatting violations
* Run black on the whole generated project & fix issues
## Description
This is the same as the pull request #1693 with the master branch merged into it to avoid all the extra unrelated commits which are already in master. Looks like Github is getting confused due to a rebase on that branch, which make that PR hard to review...
## Rationale
See #1693 - Locally, Redis is necessary only if Celery is used, while in Production it's also used for Caching.
## Use case(s) / visualization(s)
Fixes#1691
* Add failing test for travis.yml
I see three options to test travis.yml :
1. Testing that the YAML contains relevant value. Least useful and least
reliable, but simplest to implement.
2. Testing that the YAML is valid TravisCI YAML. Unfortunately this is
difficult / impossible. Doing 'travis lint' would succeed, this command
does not check for 'script' key presence and wouldn't be useful for us.
We could use 'travis-build' to verify that the YAML can be converted to
a worker config, but as of now 'travis-build' doesn't work out of the
box.
There is a new tool for validating travis YAML files 'travis-yml', but
as of now it's a ruby-only library and it's still a work in progress.
3. Running Travis CI task based on the generated YAML. This seems the
best approach, however since cookiecutter-django itself uses Travis CI,
that would require running Travis CI from within Travis CI.
Scheduling Travis CI job without a github push still requires a public
github repo, which is something that we can't generate on demand.
Given that I'm opting to use approach 1.
* Adds missing config to generated .travis.yml
The keys added are as follows:
1. 'script'
Required by Travis, cookiecutter-django used to provide it until it has
been removed together with hitch.
I'm assuming hitch has been replaced with pytest, I'm setting pytest as
the new value for the 'script' key.
2. 'install'
Not required by Travis, but necessary in our case; installs test
libraries, mostly pytest.
As of now this points to 'local.txt' requirements file. There used to be
a separate 'test.txt' requirements file but it has been decided to merge
it with 'local.txt', see discussion in
https://github.com/pydanny/cookiecutter-django/pull/1557 .
* Update CONTRIBUTORS.rst
