SYWEB-63: Fix desktop notification message when notifying for an image.
SYWEB-45: Display the user_id of a user when hovering over their avatar next to their messages.
Add notification-service.js to handle binging/notifications. Shift logic to this service.
Factor out notification logic.
SYWEB-102: Fix desktop notification msg when a user with no display name joins a room.
Make prev_event signing work again.
Remove unused sql file.
Remove unused signature storage methods
Sign evnets
Bump version numbers and change log
Merge branch 'release-v0.4.2' of github.com:matrix-org/synapse into develop
Use python logger, not the twisted logger
Merge branch 'develop' of github.com:matrix-org/synapse into federation_authorization