Summary:
This implements a form of row-level access control where for a
given table, you may specify that only owners have access to
rows for which a given column has falsy values.
For simplicity:
* Only owners may edit that table.
* Non-owners with the document open will have forced
reloads whenever the table is modified.
Baby steps...
Test Plan: added tests
Reviewers: dsagal
Reviewed By: dsagal
Differential Revision: https://phab.getgrist.com/D2633
