Added logic to wire-up the 'Add new item...' button to prompt the use…

…r for the new item when clicked, and to update the <ListWidget> 'state' field 'items' to a new array of items including the just-added item, to cause it to be re-rendered by React with that new item.

webpack_in/entry.jsx

@@ -98,7 +98,23 @@ class ListWidget extends React.Component {
                </ul>
              </div>
              <div>
                <ButtonWidget caption="Add new item..." />
                <ButtonWidget caption="Add new item..."
                              onClick={() => {
                                  const strItemNew = prompt("Please enter new item to add:",
                                                            "Item "
                                                                + (this.state.items.length + 1));
                                  if (strItemNew === null) {
                                      return;
                                  }

                                  this.setState({
                                      ...this.state,
                                      items: [
                                          ...this.state.items,
                                          strItemNew
                                        ]
                                    });
                                }}/>
                <ButtonWidget caption="Edit item..." />
                <ButtonWidget caption="Remove item..." />
              </div>