Respect default model ordering

[stevelacey]

The default ordering specified on a model does not appear to be respected by views, probably something to do with how we set custom ordering, perhaps worf is nulling it out.

Specifically this can be seen on dataset APIs in guild where we've customized the queryset to repeat the default sort for CountryList, RoleList, etc.

Expected behavior: Worf uses the model's default ordering unless ordering has otherwise been customized via the queryset or ordering view attrs.