Create a use case illustrating thematically connected statistics

[KonradUdoHannes]

The datenguide API contains many different statistics that naturally group into familiar topics. In order to help users of the package to familiarize themselves with the available statistics it would be nice to have a use case illustrating different topic specific statistics in terms of availability (what statistics exist for a topic) and content (what is the content of these statistics).

Some prior work on this was done and a text file is already present in the use case folder. The file is called topic_related_datasets.txt and contains two topics.

The naming of the statistics codes already provides a little bit of guidance as the lexicographical sorting of the codes already groups topics together in a certain wait. This could also be illustrated in the use case, but there do exist also topics not covered by the statistic codes.