Common namespace between vre-language and vre-middleware

After installing vre-middleware and vre-language together in the same virtual environment the python path to the one (totally randomly) of the packages is hidden. This causes that the modules of the one package cannot be found and imported. Separately both packages work.

We have a common namespace issue that is described here:

1. https://stackoverflow.com/questions/63722558/different-python-packages-with-the-same-top-level-name
2. https://stackoverflow.com/questions/1675734/how-do-i-create-a-namespace-package-in-python
3. https://packaging.python.org/en/latest/guides/packaging-namespace-packages/