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 download functionality to the API v2, returning
pre-signed S3 URLs that provide secure, time-limited access to document
files similar to what happens in the API v1 download document endpoint.
