Curation UI: Behaviors related to [Delete] mask button click

### Description
Currently user can click [Delete] button in the mask sections (both merging and excluding) to delete the mask entries on the CSV file in the background, but there is no feedback that the action has happened/succeeded.

- [ ] Similarly to the message shown above the [Save] button, add a feedback message says "mask has been deleted" once the action has succeeded.
- [ ] Consider delete the corresponding actual mask (shape) layer in the layer list of the napari UI

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### Size
M?

### Additional notes
V1 deliverable?