Added proper PATHs, nr of processes and cmake command.

Otherwise an error occurs during `cpack` operation due to restricted access to
/usr folder.

Resolves #495

The latest pip documentation recommends using `pip wheel` command to make the
wheel; see <https://pip.pypa.io/en/stable/cli/pip_wheel/#pip-wheel>.

This has also the advantage that the Python packages `build` and `setuptools`
are no longer required to build the wheel.

The new command is
```
python3 -m pip wheel <build-dir> --no-deps --wheel <output-dir>
```

This reverts commit 367355ab.

Merging branch 'jwu2'  into 'main'.

See merge request !1505

Merging branch 'jwu1'  into 'main'.

See merge request !1504

Merging branch 'changelog2'  into 'main'.

See merge request !1503

[i504] fix discrepancies betwee plot_int and ba_plot (#504); protect a pointer by ASSERTs (Closes #504)

Merging branch 'i504'  into 'main'.

See merge request !1501

Merging branch 'i502'  into 'main'.

See merge request !1500

Merging branch 'distr201'  into 'main'.

See merge request !1498

Merging branch 'distr201'  into 'main'.

See merge request !1497

Merging branch 'distr200'  into 'main'.

See merge request !1496