Occaisonally persist unpersisted presence updates

Don't notify for online -> online transitions.

Specifically, if currently_active remains true then we should not notify
if only the last active time changes.

Fix push room names for rooms with only an alias

Noop get_new_messages_for_device if token hasn't changed

Use state handler instead of get_users_in_room/get_joined_hosts

Add new direct message storage functions to slave store

Start adding store-and-forward direct-to-device messaging

Fix room name in email notifs

Avoid pulling the full state of a room out so often.

Fix None check in backfill