Define and measure duration for text notifications in milliseconds

During a game notification duration should be the same regardless of
game speed. Switch to using wall-clock time defined in milliseconds 
instead of game ticks. Also use the opportunity to rename the field 
to "Duration" because "RemoveTime" is not so clear.

mods/ts/chrome/ingame-transients.yaml

@@ -8,6 +8,6 @@ Container@TRANSIENTS_PANEL:
 		TextNotificationsDisplay@TRANSIENTS_DISPLAY:
 			Width: PARENT_RIGHT
 			Height: PARENT_BOTTOM
-			RemoveTime: 100
+			DisplayDurationMs: 4000
 			LogLength: 5
 			HideOverflow: False