Add data_set_name preview to data_set admin form

- Grabs the values of data_group and data_type bound to a change event on those drop downs
- populates a <p> tag to show a preview
- BUG / TODO: Doesn't update the preview when a new data group/type is added to the form. I think this is because whatever django magic that adds this new select option in is swallowing the event, so the name preview function does not trigger