This PR is handles the changes required to support envelopes. The new
envelope editor/signing page will be hidden during release.
The core changes here is to migrate the documents and templates model to
a centralized envelopes model.
Even though Documents and Templates are removed, from the user
perspective they will still exist as we remap envelopes to documents and
templates.
Fix webhooks being sent twice due to duplicate frontend calls
Updated the assistant confirmation dialog so the next signer is always
visible (if dictate is enabled). Because if the form is invalid (due to
no name) there is no visual queue that the form is invalid (since it's
hidden)
## Notes
Didn't bother to remove the weird assistants form since it currently
works for now

## Tests
- Currently running locally
- Tested webhooks via network tab and via webhook.site