add events for sib-form-file

What needs to be done?

We need to be able to listen to events when the solid-form-file uploads a file, or removes it.

What should be the event names?

upload: fileUploaded, uploaded, ...?
removed: fileRemoved, removed, ...?

Other events in sib-core:

resourceSelect
resourceDeleted
formChange
save
populate

I tend to think fileUploaded and fileRemoved are more accurate.