Merging branch 'j.0'  into 'main'.

See merge request !2287

Merging branch 'a.fixVersiondocs'  into 'main'.

See merge request !2285

After the removal of the old Python-API, the Python package must be built so
that it can be used to produce the Example figures.

Merging branch 'j.1'  into 'main'.

See merge request !2284

Merging branch 'j.1'  into 'main'.

See merge request !2283

Merging branch 'a.addPyCoreTests'  into 'main'.
related to issue #223

See merge request !2274

To avoid a clash with the system's default Python, a virtual enviroment (Python venv)
is created and employed.