derived from the participant id in addition to the salt, separated by a null
byte to avoid ambiguity attacks along the lines of
  (someRoom, someParticipant)
  (someRoo, mSomeParticipant)

Moveѕ e2ee operations to a worker that is included as text/blob for now
to simplify deployment.

fixing some minor issues and updating the description of the behaviour
when there are decoding errors

adds a document describing the high-level design of the current e2ee approach