Add a Flask-based backend

See merge request !4

Also, add Font Awesome font

- Python code (app __init__.py, main.py, config model)
- Alembic migrations
- Docker config (Dockerfile, entrypoint, Docker Compose file)
- Requirements (alembic, Flask, SQLAlchemy)
- Ignore files (Git, docker)

Closes #5

Add more services

See merge request !1

Add useless navbar

See merge request !3