Various python code quality and readability improvements
Noteworthy are:
The db model upgrade to the sqlalchemy2 syntax, giving full type information. NB the package types-sqlalchemyhas to be removed, potentially also from the servers if it doesnt happen automatically (this package is only intended for sqlalchemy 1.4, sqlalchemy2 has its type info included).
The use of a new package sphinxcontrib-httpdomain for more conveniently documenting the api endpoints in sphinx
SURVEY_DATABASE_URI is still a required config entry, but as the format isn't checked, it can be left empty, as in the config-example.json file. Should be clear enough.
