Enable Escape & Enter for confirm dialog when delete a component

Closes #1038
Fixes #1037 

appinventor/appengine/src/com/google/appinventor/client/editor/simple/components/MockComponent.java

@@ -39,6 +39,8 @@ import com.google.appinventor.shared.simple.ComponentDatabaseInterface;
 import com.google.appinventor.shared.storage.StorageUtil;
 import com.google.gwt.event.dom.client.ClickEvent;
 import com.google.gwt.event.dom.client.ClickHandler;
+import com.google.gwt.event.dom.client.FocusEvent;
+import com.google.gwt.event.dom.client.FocusHandler;
 import com.google.gwt.event.dom.client.KeyCodes;
 import com.google.gwt.event.dom.client.KeyUpEvent;
 import com.google.gwt.event.dom.client.KeyUpHandler;
@@ -46,6 +48,7 @@ import com.google.gwt.user.client.Command;
 import com.google.gwt.user.client.DOM;
 import com.google.gwt.user.client.DeferredCommand;
 import com.google.gwt.user.client.Event;
+import com.google.gwt.user.client.Event.NativePreviewEvent;
 import com.google.gwt.user.client.Random;
 import com.google.gwt.user.client.Window;
 import com.google.gwt.user.client.ui.Button;
@@ -248,6 +251,20 @@ public abstract class MockComponent extends Composite implements PropertyChangeL
 
       add(contentPanel);
     }
+    @Override
+    protected void onPreviewNativeEvent(NativePreviewEvent event) {
+      super.onPreviewNativeEvent(event);
+      switch (event.getTypeInt()) {
+        case Event.ONKEYDOWN:
+          if (event.getNativeEvent().getKeyCode() == KeyCodes.KEY_ESCAPE) {
+            hide();
+          } else if (event.getNativeEvent().getKeyCode() == KeyCodes.KEY_ENTER) {
+            hide();
+            MockComponent.this.delete();
+          }
+          break;
+      }
+    }
   }
 
   // Component database: information about components (including their properties and events)