Halved the number of snapshots occurring at replay time by preventing our eventMessage construction code from running in replay window.
Now storing only divergences in the eventMessage, rather than storing snapshot of the whole DOM.
Content script now turns off record-timed snapshoting when in replay tab, but maintains most recent divergence (calculated for synthesis) to be used in creating eventMessage for the replayed event.  The eventMessages for replayed events are used when a replay session is being sent to the server.