Global error handler

[lukashornych]

Currently, any exception that is not manually catched and handled is lost in console log. This is not good for UX, normal user will not notice such error, only unresponsive UI.

Vue lets us register global error handler https://vuejs.org/api/application.html#app-config-errorhandler. We could use this to catch any unhandled error and create fallback toast error notification.