Summary:
This moves some more tests to core that would be useful for ANCT,
which had been stuck in grist-saas due to some entanglements with
sendgrid and billing. For sendgrid, I've moved around just enough
material to permit the tests to run mostly unchanged. Ideally
the interface to a notification system would be generalized, but
that's a bigger project.
Test Plan:
checked that tests are likely to run as expected
in core using preview laid out by ./buildtools/build_core.sh
Reviewers: georgegevoian
Reviewed By: georgegevoian
Differential Revision: https://phab.getgrist.com/D4149
