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)

But I'd rather you not use isinstance() if you don't have to. 

http://stackoverflow.com/questions/1952464/in-python-how-do-i-determine-if-an-object-is-iterable has some alternatives, including using hasattr() to look for the iter and getitem magic methods, calling iter() on it and catching the exception, or just assuming it's iterable and catching the exception.

If this check isn't here and the thing returned isn't a container type, what happens?