Python-base-app

* Fix YAML syntax in circle-ci.yml
* Set `TEST_PYPI_EXTRA_INDEX` correctly in generic installation script

* Supply metadata for all contribution packages in `base_ci_toolbox.py`
* Provide new Docker image build arguments `BRANCH` and `REPO_DOWNLOAD_BASE_URL`
* Fixes to `generic-install.sh`:
* Use correct path to `pip3.sh` script
* Download Pip packages of project and all contribution libraries
* Swap deploy and docker stages in CI jobs
* Do not output pip version (collides with wrapper script)
* Closes [LittleBrother 170](https://github.com/marcus67/little_brother/issues/170)

* Dump stack trace for all general exception in `base_ci_toolbox.py` (for debugging in Circle CI)
* Fix configuration for `publish_pypi_package` in `setup.py` of test resources (triggered run time error in release builds)

* Switch all images for all staged to `marcusrickert/docker-python-app`
* Use symbolic link for `requirements.txt` in test resources

* Optionally delete existing PyPi packages on GitLab before uploading (effectively replacing them)

* Improve testing of `Pinger`
* Deactivate physical ping tests with environment variable `NO_PING`