Closing the last <window> should not exit the application

[mhink]

This has been bothering me for awhile. I'm quite sure there's a reasonable way to prevent this from happening, I just need to buckle down and do it.

[Vlemert]

This can be very easily done by setting an event handler for window-all-closed on the app:

this.rootContainer.app.on('window-all-closed', () => {
  // noop
});

Though I must say that I think this is only the expected behaviour on mac, so maybe it should check for that, or allow the user to enable/disable this using a prop?