New integrations

[AntonDnepr]

A lot of new features:

• Flake8 integration
• Pre-commit
• Prospector
• Custom user model (we need one in every project I assume)
• Black
• Factory boy
• pytest-mock
• Scripts for the Pipenv
• Media files auto removal for the tests
• Separate config file for tests

Fixes:

• Celery removal from settings
• Dynamic ports for docker (default config fails for me, I have more than 1 project with docker, so it is must-have)
• coverage changes
• Dynamic DB user for docker
• Removal of pytest-cov (critical bugs and nothing we can't achieve without it)
• SECRET_KEY fix
• Celery removal from the settings
• Update for docs

Controversial changes (I'm not sure about them):

• Current .env.examples for database and redis didn't work for me, so I've changed them into workable one. Though I'm not sure if the old format was workable and I just didn't run it correctly somehow

I need elaborate on task.py changes: I make things less configurable for circle.ci and just run the Pipfile scripts instead:

• First line create a coverage using py.test
• Second one show the coverage report and exit with non zero code if the coverage is less than 95%. It makes pipelines on the bitbucket fail (because of non 0 code command finish), but I'm not sure if the same thing will work for the circle.ci. Though, I assume it should be.

Concerns I removed docker-dns, as overkill but we can return it I'm not sure if we need invoke at all, if we have powerful scripts support inside Pipenv itself

[jensneuhaus]

Okay, can be merged - I leave it up for you.