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/Themes/default/metrics.ini

@@ -11,12 +11,13 @@ CourseDifficultiesToShow=easy,regular,difficult
 StepsTypesToHide=dance-couple,dance-solo,pump-halfdouble,lights-cabinet
 ScreenWidth=640
 ScreenHeight=480
-OverlayScreens=ScreenSystemLayer,ScreenDebugOverlay
+OverlayScreens=ScreenSystemLayer,ScreenSyncOverlay,ScreenDebugOverlay
 EditMode=2
 MaxCourseEntriesBeforeShowVarious=6
 
 [Screen]
 InitCommand=
+AllowOperatorMenuButton=0
 
 [ModeSwitcher]
 PrevModeX=-200
@@ -2249,7 +2250,7 @@ StatsY=SCREEN_TOP+10
 StatsOnCommand=horizalign,right;vertalign,top;zoom,0.5;shadowlength,2
 MessageX=0
 MessageY=0
-MessageOnCommand=finishtweening;horizalign,left;vertalign,top;x,SCREEN_LEFT+4;y,SCREEN_TOP+4;zoom,0.8;shadowlength,2;diffusealpha,1;x,-SCREEN_WIDTH;linear,0.5;addx,SCREEN_WIDTH
+MessageOnCommand=wrapwidthpixels,800;finishtweening;horizalign,left;vertalign,top;x,SCREEN_LEFT+20;y,SCREEN_TOP+20;zoom,0.8;shadowlength,2;diffusealpha,1;addx,-SCREEN_WIDTH;linear,0.5;addx,SCREEN_WIDTH
 MessageOffCommand=sleep,5;linear,0.5;diffusealpha,0
 TimeX=SCREEN_LEFT+4
 TimeY=SCREEN_TOP+40
@@ -2266,6 +2267,10 @@ CreditsJoinOnly=0
 Class=ScreenDebugOverlay
 Fallback=Screen
 
+[ScreenSyncOverlay]
+Class=ScreenSyncOverlay
+Fallback=Screen
+
 [WheelItemBase]
 TextOnCommand=
 TextX=0
@@ -4545,3 +4550,8 @@ NumbersY=0
 
 [ScreenBranch]
 Fallback=Screen
+
+[ScreenSaveSync]
+Fallback=ScreenPrompt
+Class=ScreenSaveSync
+NextScreen=@GetGameplayNextScreen()