Summary:
* Adds a simple deployment test for the "Import from URL" button.
* Makes server aware of plugin hostnames in the appropriate places.
* Unrelated but convenient: allows following redirection when importing.
Test Plan:
Added tests. The `local_deployment` test works. A modified
version of this works against `staging_deployment` (using a test url that
doesn't require redirection; also staging currently has a hot fix that can
hopefully be removed once the code fix included here is in).
Reviewers: dsagal
Reviewed By: dsagal
Differential Revision: https://phab.getgrist.com/D2556
Summary: This moves enough server material into core to run a home server. The data engine is not yet incorporated (though in manual testing it works when ported).
Test Plan: existing tests pass
Reviewers: dsagal
Reviewed By: dsagal
Differential Revision: https://phab.getgrist.com/D2552
