Summary:
After the welcome questions are dismissed, a video tour modal will
now be displayed. The video tour is also accessible via a tool button
in the left panel of the home page, as well as a text button next to
the Examples & Templates header.
Test Plan: Browser tests.
Reviewers: dsagal
Reviewed By: dsagal
Subscribers: dsagal
Differential Revision: https://phab.getgrist.com/D3477
