Implement cut tool

yeah that was the easy part but still

- Added hotkeys for copy, paste and cut
- Added _copyPaste.js for copy, cut and paste management

js/_mouseEvents.js

@@ -355,7 +355,7 @@ function draw (mouseEvent) {
 
         // If I'm dragging, I move the preview
         if (dragging && cursorInSelectedArea()) {
-            updateMovePreview(mouseEvent);
+            updateMovePreview(getCursorPosition(mouseEvent));
         }
     }
 }