This updates the datagrid querysets to set distinct=False and to omit

with_counts=True. This simplifies the base querysets for all the

datagrids, ensuring that the datagrid code can generate a slim and

efficient queryset for computing total item counts for pagination. Prior

to this, the querysets were in the form of:

SELECT COUNT(*) FROM (SELECT DISTINCT ...);


That was causing all results to be fetched and then for a total count to

be computed based off that. Certainly not efficient, and the source of

problems in the past for some users.
The data queryset still uses distinct, which is set by the datagrid code

itself. Although we can now turn this off, we are going to keep it on

for now, with plans to test removing the distinct flag for querysets in

Review Board 7.

Unit tests pass.
Been testing all the datagrids with this change, ensuring that the counts

seem fine and that there are no noticeable regressions.