#11 and #3: added more readable REST API for controlled_vocabulary (and also for requests of only one entry))

#4: bug fix done for nested stationmeta (inside timeseries record); still left to do: clean up of code and adapting pytests

#11 and #3 (and also #8): provided an API to the controlled vocabulary (as long as no ontology service is in place), also wrote first pytest, but not yet working (settings have to be established in test database), prepared scripts to create pages also documenting the controlled vocabulary (pages: index can still show the source code, which is wanted)

#11: still struggling with creating pdf (but now a little bit better) -- see (pandoc) command in issue

#11: started adding descriptive text for automatic openapi documentation (especially for use documenting metadata)