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

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

#4: nested upload for stations done; TBD: more testing (esp. pytest), use controlled vocabulary (related to #3)

#4: nested download for stationmeta realized; TBD: uploading of new test database, nested download for stationmeta

#8: common base and test base is in place (but teardown of test_base has to be worked on for chained pytests)

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