[Deployment] Flask-SQLAlchemy updated to 3.0.0

Flask_Alchemy undergone a huge update with long CHANGELOG.

There seem no breaking changes for us on a first quick test. Never the less, we have to test the current version against the new one to see, if we can do the update on the server.

They also have a new function called one_or_404 similar to get_or_404 or first_or_404. We have to see, if it is useful to us. We use get_or_404 and first_or_404 a lot ...