Add auth module stub, seam, and requirements.
Address review comments and simplify tests.
Add settings mechanism.
Update settings mechanism to work better under test; address review comments
Move auth -> third_party_auth to avoid import collisions; add LinkedIn provider
Address review comments; remove boilerplate
Address review comments: rename patch; add pylintrc changes; remove pylint suppressions; discover subclasses outside provider.py
Address review comments: move apply_settings into startup.py.