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.
Adds document access tokens and QR code functionality to enable secure
document sharing via URLs. It includes a new document access page that
allows viewing and downloading documents through tokenized links.
