Summary:
Clearing virtual tables after user navigates away from the pages
that show them. Leaving them behind will reveal them on the Raw
Data page, with a buggy experience as user can't view the data
there.
Test Plan: Extended tests.
Reviewers: paulfitz
Reviewed By: paulfitz
Subscribers: jarek, georgegevoian
Differential Revision: https://phab.getgrist.com/D4258