Add warning when user is about to leave page with unsaved changes

Currently, when you are reviewing, it is possible that the user (accidentally) leaves the page without having saved what he/she typed. It would be a nice improvement to add a warning when the user wants to leave the page, but there are unsaved changes. Navigation Guards in Vue might help: https://router.vuejs.org/guide/advanced/navigation-guards.html#in-component-guards