#3: added unique constraint to controlled vocabularies; added foreign keys (controlled vocabularies) to models

#3,#4: nested uploads/downloads using controlled vocabulary; still to investigate: how to load enum_tables at beginning (this commit is a workaround)

almost done: using human readable controlled vocabulary for upload; TBD: using human readable controlled vocabulary for download, adapting pytests

#4: defined association tables also in models; now using one base for the whole app 'toardb'; this has now also to be adapted to test_base

#4: nested upload/download for roles (timeseries) working in production and pytest (uploading codes not human readable version)

#4: a typo made my days and nights long; after git crash do another upload; now detangling models_core and models_role again (different source code files)

#4: code completely messed up, but nested upload working; nevertheless download is NOT returning the nested view

#2: many-to-many relationship for role codes seem to work now within FastAPI; will probably again not work with pytest; has to be cleaned up again: just storing before crash

created ONE toardb app, also adapted pytests for toardb app (still very last test will throw an error for teardown; inserted example for url percent encoding