* Ensure non-thread relations to a thread root are actually in both timelines
* Make thread in sendReceipt & sendReadReceipt explicit rather than guessing it
* Apply suggestions from code review
* Fix Room::eventShouldLiveIn to better match Synapse to diverging ideas of notifications
* Update read receipt sending behaviour to align with Synapse
* Fix tests
* Fix thread rel type
* Fix mark as unread button
* Revert to prefer the last event from the main timeline
* Refactor room test
* Fix type
* Improve docs
* Insert events to the end of the timeline
* Improve test doc
* Fix issue where the root event of a thread had to be loaded in a complicated way
* Fix issue where edits to the last event of a thread would get lost
* Fix issue where thread reply count would desync
* Refactor relations pagination mocking for tests