cleanup: do Session.add directly inside _create_default_perms Let the various _create_default_perms functions add the created object to the SQLAlchemy database session, instead of having the caller do it. This is in accordance with the Kallithea contribution guidelines: When creating an object using a factory function (like create_repo), the returned object has already (by convention) been added to the session, and should not be added again.

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
.