Modify multiple participants at once, either by sending a message to change state, or by changing the local view.

updateParticipants() batches the changes together, speeding up the updates. Use this method instead of looping over updateParticipant().

The propertiesObject's keys are participant session ids and values are the actions described in updateParticipant() and their corresponding values. Internally, this method just loops over the keys and calls updateParticipant() multiple times.

Returns this.