Sorting by "id" has the same effect as sorting by created_at while
performing far better and without the need of an extra index (in case
one wanted to speed up sorting by "created_at").
Sorting by "Recently updated" still uses the physical "updated_at"
column as there's no way to use the "id" column for this instead.
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.
