* Make the roomserver output format more flexible

* Fix the sync server integration testdata

* Fix roomserver testdata

* Actually fix the sync server tests

* Fix typo

* Add test for transition to leave

* Add test for join/leave in the same /sync response

- Test data for the sync server is now in its own file.
- Rejig the sync server tests to support multiple /sync requests and corresponding
  assertions.
- Fixed a minor bug which resulted in state events to appear twice in /sync
  responses when syncing without a `since` parameter.