Add `ordered` scope for Design

!17788 (diffs, comment 230875678) introduced an .order for ordering of Designs.

As mentioned in the above thread, once that MR is merged we should:

• Add an ordered scope for Design
• Update DesignsFinder to be able to use it
• Ensure that the scope is being used when returning Designs in GraphQL

Optional: Look into whether we should officially start ordering designs by filename by having the ordered scope be order(:filename).order(id).