Merge branch 'develop' into release-v0.27.0

CHANGES.rst

synapse/app/appservice.py

synapse/app/client_reader.py

synapse/app/event_creator.py

synapse/app/federation_reader.py

synapse/app/federation_sender.py

synapse/app/frontend_proxy.py

synapse/app/homeserver.py

synapse/app/media_repository.py

synapse/app/pusher.py

synapse/app/synchrotron.py

synapse/app/user_dir.py

synapse/handlers/register.py

synapse/http/server.py

synapse/python_dependencies.py

synapse/state.py

synapse/storage/events.py

synapse/storage/group_server.py

synapse/storage/registration.py

synapse/util/httpresourcetree.py