🎨 Bring Python code into compliance with Black and Flake8 (#121)

* Ignore Flake8 unused import error F401

https://flake8.readthedocs.io/en/latest/user/error-codes.html

The apparently unused imports may be needed for SQLAlchemy.

As the code comment says:

make sure all SQL Alchemy models are imported before initializing DB
otherwise, SQL Alchemy might fail to initialize properly relationships

See GitHub 28 and 29

* Ignore Flake8 unused variable error F841

https://flake8.readthedocs.io/en/latest/user/error-codes.html

The apparently unused variables may be needed for tests.

* Bring line length into compliance with Black

Should be 88 characters.

* Format alembic code with Black

{{cookiecutter.project_slug}}/backend/app/alembic/env.py

@@ -67,11 +67,9 @@ def run_migrations_online():
 
     """
     configuration = config.get_section(config.config_ini_section)
-    configuration['sqlalchemy.url'] = get_url()
+    configuration["sqlalchemy.url"] = get_url()
     connectable = engine_from_config(
-        configuration,
-        prefix="sqlalchemy.",
-        poolclass=pool.NullPool,
+        configuration, prefix="sqlalchemy.", poolclass=pool.NullPool,
     )
 
     with connectable.connect() as connection: