Add basic User auth endpoints (non functional)

See merge request !5

A user actually only has a uuid and a name, this is because we look all relevant data up in LDAP.

We only save the User, so that we can re-identify them even if e.g. their login changes

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)