Django-migration-linter

* Add possibility to lint newly generated migrations through the `makemigrations` command.
You can activate it through the `--lint` command option, or by default with the `MIGRATION_LINTER_OVERRIDE_MAKEMIGRATIONS = True` Django settings.

* Handle making a column NOT NULL with a Django default value as backward incompatible.
This should have been the case from the beginning, but it was not.
When one uses the `django-add-default-value` lib, the operation should still be compatible.
* Improve behaviour of the `--include-migrations-from` option.
When the given filename is missplelled, fail instead of linting all migrations.
When the file is empty, lint no migrations instead of linting all migrations.
* Update libraries used for testing (`tox`, `flake8`, etc.)

* Don't pin dependencies but only define minimal versions

Fixed bug:
* Correctly detect `apps.get_models` when on multiple lines in data migration

* Make summary output more friendly (Thanks to vald-phoenix)
* Add forgotten documentation about `IgnoreMigration`
* Don't pin the `appdirs` strictly to 1.4.3, but allow higher versions

* Detect in data migrations if models are imported the correct way or not