Undo and Redo Operations Functional, with some caveats

SpriteMapEditor/SpriteMapModifications/ISpriteModification.cs

@@ -1,14 +1,19 @@
 using System;
 using System.Collections.Generic;
+using System.Windows.Forms;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 
 namespace SpriteMapEditor.SpriteMapModifications
 {
-    interface ISpriteMapModification
+    public interface ISpriteMapModification
     {
         void Do();
         void Undo();
+        List<int> GetPreChangeSelection();
+        void SetPreChangeSelection(List<int> currentSelection);
+        List<int> GetPostChangeSelection();
+        void SetPostChangeSelection(List<int> currentSelection);
     }
 }