Add toast or snackbar

[loloof64]

Hi ! I think it would be great if we could show a kind of in-app notification, like a simple Toast (e.g the Toast from Jetpack Compose framework) or Snackbar (e.g the Snackbar from Flutter framework).

The advantage of such in-app notifications, is that the can be automatically closed after a short amount of time (an so the user may avoid be distracted by the messages flow).

[bjorn]

I have implemented part of such a widget in my app as follows:

https://github.com/bjorn/raccoin/blob/c1198b61c5b29cdc31b0c1599064149b1d485d74/raccoin_ui/ui/appwindow.slint#L171-L200

The backend can push a notification into the model, and the UI removes it by index. The part which I didn't implement yet is to automatically hide the notification after a timeout, and there is no animation.

[loloof64]

Thank you very much. So I'll have a look at it, and try to add the automatic closing feature. Having animations or not does not matter so much for me 😃 .