Sometimes cancelled requests show up again at the next progress update

[DavidQuartz]

When the user cancels a request there's a time window where the backend still returns the progress for the cancelled resource.
This causes a flickering: the client removed the card but it shows up again when it received the new progress, still containing the cancelled upload.
Two alternative solutions:

• we show a message of the cancelling in progress, as we have for delete, etc.
• we hide the card as we do now, but we stop tracking the progress for the selected element

In both cases the client has to keep track of the cancelled uploads.