By moving the default sort order into a separate scope (and calling this
from the default scope) we can more easily re-apply a default order
without having to specify the exact column/ordering all over the place.
Sorting by both "created_at" and "id" in descending order is not needed
as simply sorting by "id" in descending order will already sort rows
from new to old. Depending on the query and data involved sorting twice
can also introduce significant overhead.
