Summary:
Adds a "Duplicate Table" menu option to the tables listed on
the Raw Data page. Clicking it opens a dialog that allows you to
make a copy of the table (with or without its data).
Test Plan: Python, server, and browser tests.
Reviewers: jarek, paulfitz
Reviewed By: jarek, paulfitz
Subscribers: jarek
Differential Revision: https://phab.getgrist.com/D3619
