Restructure IntelliO3 refrerence download

In #131 we made IntelliO3-ts v1.0 available as reference forecast (see mlair/reference_data_handler/). Currently, we use os.system(tar ...) to extract forecasts from the tar.gz file published on https://b2share.eudat.eu/records/5042cda41a4c49769cc4010d231ecdec

We should replace the os. commands with the tarfile package.