Sjang92/advanced settings feedback

@jrbl  @njdup

There were no validations being done in Studio's course advanced settings tab. 
Now course instructors receive feed back as a list of settings changes that has formatting/value errors.

![screen shot 2014-07-16 at 4 13 13 pm](https://cloud.githubusercontent.com/assets/3598201/3606958/e8fe92b8-0d3e-11e4-8fe6-b861b0a8b3d4.png)

If you are sending back JSON (which makes sense), use JsonResponse. You can specify the error status when creating it. Or it might be nice to create a JsonResponseBadRequest class in json_request.py (where JsonResponse lives).