Added navigation within lightbox

You can have links inside the lightbox to navigate to another url, without closing the lightbox.
In order to do that, you only have to add the links to navigate inside the content of the lighbox, with the class js-lightbox-navigation These links will open the url in the href in the lightbox
I think it's maybe worth adding more than one link and then checking that `_navigateTo` gets called with the correct one.