Summary:
* Fix old download endpoint to correctly pass org info in redirect.
* Switch to use newer download endpoint in client.
Old endpoint not removed. I started doing that, but it is used in copying, and it struck me that I'm not sure what should happen when copying from a site document to "Personal" - should it be the Personal that is associated with docs.getgrist.com currently, of should it be the Personal that is associated with the email of the user on whatever-site-we-are-on.getgrist.com. So leaving that as separate work.
Test Plan: updated tests
Reviewers: dsagal
Reviewed By: dsagal
Differential Revision: https://phab.getgrist.com/D2639