Improve upload item modal

## 🎉 Description

Improve upload item modal

* 📈 This is a feature request.

## 📝 Details

1. Once you run into an error, the error message remains in the “upload item” modal if you close it and try again with another item. You have to refresh the page to clear those error messages. They should be purged every time you open up the modal.
2. While the item is being uploaded, there’s no spinner or any kind of UI feedback that it’s being processed (you’re always wondering if something broke)
3. There are some actually helpful error messages that appear in console but that don’t make it to the UI, would be great to push these to the UI too