Always use select_related(depth=1) when fetching items in a DataGrid.

We were conditionally calling select_related(depth=1) based on sort
orders when fetching items from the DataGrid. However, in many (most?)
cases, cells are going to display data on models from foreign keys on
the object. So, we instead always call select_related(depth=1), since
it's not that much more expensive a query, but may save several
subsequent queries per row.

Tested with our various datagrids. Nothing broke, as nothing should with this query. It's just loading additional data.