Summary:
Adding sort options for columns.
- Sort menu has a new option "More sort options" that opens up Sort left menu
- Each sort entry has an additional menu with 3 options
-- Order by choice index (for the Choice column, orders by choice position)
-- Empty last (puts empty values last in ascending order, first in descending order)
-- Natural sort (for Text column, compares strings with numbers as numbers)
Updated also CSV/Excel export and api sorting.
Most of the changes in this diff is a sort expression refactoring. Pulling out all the methods
that works on sortExpression array into a single namespace.
Test Plan: Browser tests
Reviewers: alexmojaki
Reviewed By: alexmojaki
Subscribers: dsagal, alexmojaki
Differential Revision: https://phab.getgrist.com/D3077
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
