Pass around the reactor explicitly (#3385)

synapse/handlers/auth.py

synapse/handlers/message.py

synapse/handlers/user_directory.py

synapse/http/client.py

synapse/http/matrixfederationclient.py

synapse/notifier.py

synapse/replication/http/send_event.py

synapse/rest/media/v1/media_repository.py

synapse/rest/media/v1/media_storage.py

synapse/server.py

synapse/storage/background_updates.py

synapse/storage/client_ips.py

synapse/storage/event_push_actions.py

synapse/storage/events_worker.py

synapse/util/__init__.py

synapse/util/async.py

synapse/util/file_consumer.py

synapse/util/ratelimitutils.py

tests/crypto/test_keyring.py

tests/rest/client/test_transactions.py