…ase-v1.4.0

* origin/release-v1.4.0: (36 commits)
  Improve logging for a failing test (#709)
  Make 3PID binding tests use /account/3pid/bind ala MSC2290 (#703)
  Use unstable prefix for 3PID unbind API
  Add support for handling email validation challenges (#707)
  do requestToken before adding a 3pid (#706)
  Configure synapse to use the test mail server (#705)
  Implement a mail server to help with 3pid testing (#704)
  federated_rooms_fixture (#701)
  Use Sytest develop for Dendrite's master branch (#700)
  Don't assume atomicity
  Fix flakiness due to create_room_synced (#702)
  Don't require an avatar_url
  Replace HOMESERVER_INFO incantations (#699)
  add some logging for flaky sync test (#698)
  Fix problems when using hash
  Accept access_token instead of id_access_token on the IS, accept Authorization header (#697)
  Use hash and handle variable sized final chunk
  Have the in-built identity server support v2 (#689)
  Add tests for 3PID /unbind API (#691)
  Fix typo
  ...