Fix issues with incorrect email replies to event organizer

* We were previously storing the user's attendee status in the
  SYNC_ADAPTER_DATA column of the Event, but it turns out that
  this data isn't available in the Entity we retrieve when
  uploading changes to the server
* The result is that we often thought the user's status had
  changed when in fact it had not; in these cases, we sent email
  to the organizer, often with the wrong information.
* As of this CL, we store the user's attendee status in an
  ExtendedProperties row (these values are already exposed in event
  entities)
* The logic otherwise remains the same; we now get correct data,
  however

Bug: 2638762
Change-Id: Ibe8db90c16b4ca06203f77fd010aa26dde89a556
1 file changed