This should transactional snapshot isolation for `/sync` etc requests.
For now we don't use repeatable read due to some odd test failures with
invites.
* It's half-alive
* Wakeups largely working
* Other tweaks, typing works
* Fix bugs, add receipt stream
* Delete notifier, other tweaks
* Dedupe a bit, add a template for the invite stream
* Clean up, add templates for other streams
* Don't leak channels
* Bring forward some more PDU logic, clean up other places
* Add some more wakeups
* Use addRoomDeltaToResponse
* Log tweaks, typing fixed?
* Fix timed out syncs
* Don't reset next batch position on timeout
* Add account data stream/position
* End of day
* Fix complete sync for receipt, typing
* Streams package
* Clean up a bit
* Complete sync send-to-device
* Don't drop errors
* More lightweight notifications
* Fix typing positions
* Don't advance position on remove again unless needed
* Device list updates
* Advance account data position
* Use limit for incremental sync
* Limit fixes, amongst other things
* Remove some fmt.Println
* Tweaks
* Re-add notifier
* Fix invite position
* Fixes
* Notify account data without advancing PDU position in notifier
* Apply account data position
* Get initial position for account data
* Fix position update
* Fix complete sync positions
* Review comments @Kegsay
* Room consumer parameters
