This gives the calling code better control over the handling of such
errors and makes it easy to differentiate between errors and valid
return types.

This adds a string representation for all program models except the
schedule so that it is easier to identify objects in DRF’s filter,
create, and update forms.

- update the model
- migrate the model
- update the serializer
- update the views

- updated the fixture
- updated the serializer
- updated some views