See merge request !14

The version of the package is defined once in `pyproject.toml`.
The two packages `batsim` and `schedulers` now rely on `importlib` to
retrieve the version.
Refer to [1] for details.

[1]: https://packaging.python.org/en/latest/guides/single-sourcing-package-version/

Sphinx is required to build documentation.

This commit removes `launcher.py` and `launch_expe.py` as they are
redundant with the console scripts defined in `setup.py`.

Namely, `launcher.py` is installed as `pybatsim` and `launch_expe.py` is
installed as `pybatsim-experiment`.

These are not hardlinks but kind of particular refcounters

That was causing a return value of 1 in some cases