made an action for the 'fit to screen' feature

Source/Editing/ClassicMode.cs

@@ -225,6 +225,7 @@ namespace CodeImp.DoomBuilder.Editing
 		}
 		
 		// This zooms and scrolls to fit the map in the window
+		[Action("centerinscreen", BaseAction = true)]
 		public void CenterInScreen()
 		{
 			float left = float.MaxValue;

Source/Resources/Actions.cfg

@@ -167,6 +167,15 @@ zoomout
 	allowscroll = true;
 }
 
+centerinscreen
+{
+	title = "2D: Fit To Screen";
+	description = "Zooms out the map and centers it to make it completely fit in the screen, giving a high overview of the map.";
+	allowkeys = true;
+	allowmouse = true;
+	allowscroll = true;
+}
+
 gridsetup
 {
 	title = "View: Grid Setup";