sync controls cleanup:

move sync display/saving out of complicated ScreenGameplay
  show sync UI in editor playback as well as gameplay
  revert sync from in-memory backup, not from disk
  move more functions into debug overlay

stepmania/src/MessageManager.cpp

@@ -46,6 +46,8 @@ static const CString MessageNames[] = {
 	"SideJoinedP1",
 	"SideJoinedP2",
 	"PlayersFinalized",
+	"AssistTickChanged",
+	"AutosyncChanged",
 };
 XToString( Message, NUM_MESSAGES );