Merge pull request #106 from matrix-org/application-services-txn-reliability

synapse/appservice/__init__.py

synapse/appservice/api.py

synapse/appservice/scheduler.py

synapse/handlers/__init__.py

synapse/handlers/appservice.py

synapse/storage/__init__.py

synapse/storage/appservice.py

synapse/storage/schema/delta/15/appservice_txns.sql

tests/appservice/test_scheduler.py

tests/handlers/test_appservice.py

tests/storage/test_appservice.py