added nonfunctional --live-replay option, refactored eventlog and player:

 - --live-replay is ignored when a terminal is joining
 - eventlog doesn't send WRITE events when in --live-replay mode
 - _do_live_replay shim in Player
 - TODO: still need to connect past user input to a live pty
 - TODO: still need to insert live output from the pty in the terminal