This enhances the datagrid unit tests to use assertQueries() instead

of assertNumQueries(). This gives us greater insight into the queries

being executed when rendering a datagrid, and will help with performance

tuning going forward.
A number of datagrid unit tests lacked any query-related assertions.

This change adds these, and in the process has uncovered some major

performance issues. These will be resolved in upcoming changes.

Unit tests pass.