#17, #9: patch API produces changelog entries for 'SingleValue' and 'Comprehensive' (also additions for #7 to be found in this commit)

#7: controlled vocabulary for kind of annotation was introduced (changes in crud.py and schemas.py to be found in commit for #17)

#17: REST APIs to changelog tables are build; #9: patch API for stationmeta creates a separate changelog entry for every field changed in the metadata

#17: delete coordinate_validation_status, coordinate_validation_date, and coordinate_validator_id from fixtures for pytest

#17 and #9: stationmeta patch API writes (one) entry to changelog table; schema shows changelog table when requesting stationmeta from database

#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)