[Request]: Gracefully handle limited media

[GeopJr]

Describe the request

From my understanding and investigation from a previous issue, instances that limit media from other instances, still attach them to the status objects but with broken proxied urls.

That leads to just... empty 404 attachments. Tuba should gracefully handle them by displaying them in a list and when the user clicks on them, ask them if they would like to fetch the remote URL, while warning them that their IP address will be exposed.

Implementation Details

• This follows the GNOME HIG.