Workoutset crud ajax

The front end javascript is pretty rough still, but I have added drag and drop re-ordering for the workoutsets.

Included in this:
* Drag and drop to change the order of WorkoutSet records, I didn't really care about re-ordering but it seemed like an easier place to start from than the full CRUD functionality.
 * In retrospect, I am not sure this was a good feature at all. But I wanted something relatively easy so that I could get more experience calling the django REST framework from javascript.
* It should be relatively easy now to add delete functionality to the page (arguably a much more useful feature than drag and drop).
* Big rework of the WorkoutSet REST API to support permissions checking and the django_measurement field - MeasurementField.
 * This got the endpoints working so that I could use them from the javascript side, along with maintaining a fairly uniform behavior between the REST framework and the controllers (so they are working with the WorkoutSet data using the same conventions).
I remove these tests, in an effort to maintain uniformity between the REST endpoints and the this code each record will display it's own units. The serializers at this point do not have the ability to convert all the weight units based on the user (it is possible to could follow user fk relationship to look up the data).