Fix handling of layout folders in Data API backend
Fix handling of layout folders in Data API backend

- Folders are now flattened, and just the layout names returned when
  reading from a layout via the Data API backend.

GoyaPtyLtd/RESTfm,GoyaPtyLtd/RESTfm,GoyaPtyLtd/RESTfm,GoyaPtyLtd/RESTfm