Provide default UX for requesting access in when server responds 403

The Solid system includes/should include protocols for one user to request that another user gives them access to a given resource.

Note, as background, that when a user uses a web browser to access a web server, and has logged in but has not granted access, then the server can respond with a 403 error web page which includes (for example) a button to press to request access. Then there is a protocol behind the scenes which lodges a request with the resource owner, and if the resource owner grants access, notifies the original user that access has been granted and they should try again.

When a solid user is using an app, and that app tries to access some data on their behalf, currently the user is sometimes shown a "403 unauthorized" message just as an error message.
This proposes that solid-ui should contain facilities for inserting the access request protocol in the user experience in this case.

One can imagine that the request may be granted immediately (if eg the users are in the same room and talking) or after some time. In the later case, the notification message must have enough context to allow the users to click on a link and get bak to the thing they were trying to do when they were originally blocked.

No se nombran archivos, pruebas ni puntos de entrada. Empieza revisando el manejo existente de respuestas 403 y de los widgets relacionados con el acceso en solid-ui; después, define el flujo de solicitud de acceso y notificación diferida descrito en el issue. Se considera terminado cuando la UX puede iniciar una solicitud, gestionar una aprobación inmediata o diferida y conservar un enlace al recurso bloqueado.