Fixes#1307Fixes#1132
Related to #1306
Deleted webhook notifications include the org id and item/collection id.
This PR also includes API docs for the new webhooks and extends the
existing tests to account for the new webhooks.
This PR also does some additional cleanup for existing webhooks:
- Remove `downloadUrls` from item finished webhook bodies
- Rename collection webhook body `downloadUrls` to `downloadUrl`, since
we only ever have one per collection
- Fix API docs for existing webhooks, one of which had the wrong
response body