Show Confirmation Before Builder Exit

[ElliotPenson]

Create a utility that adds a listener to the beforeunload event. This will cause a message to be shown to the user before they reload or exit the site.

window.addEventListener('beforeunload', event => {
  event.preventDefault();
  event.returnValue = '';
});

Call this utility in the componentDidMount method of Create. Remove the listener when the user publishes the fractal.