move data downloader and transformation code to own repo and simple python package

[cchwala]

Once we have a first satisfying version of the opensense_data_downloader_and_transformer.py, we should move it to its own repo so that it can easily be integrated into other software projects.

[cchwala]

I suggest to add a new repo in the OPENSENSE group, ideally using one of those python package templates that already sets up things to publish on pypi. A conda-forge version via adding a recipe has to be published, too.

[cchwala]

Based on discussion with @fenclmar, we should combine the potential package for downloading and transformation with code to check that the OPENSENSE data format conventions, which are stored at https://github.com/OpenSenseAction/OS_data_format_conventions, are obeyed.