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)

In these two lines, you refer to ```request.json[ADVANCED_COMPONENT_POLICY_KEY]["value"]``` twice; you should probably memoize it, like:
```
# Check if the user has incorrectl failed to put the value in an iterable.
policy_value = request.json[ADVANCED_COMPONENT_POLICY_KEY]["value"]
if isinstance(policy_key, collections.Iterable):
    if ac_type in policy_key:
```