The thing I'm looking for right now is to be able to say `ItemFactory.create('course', enrollment_start='Foo')`, rather than having to have `ItemFactory.create('course', fields={'enrollment_start': 'Foo'})`, because the created course will have `course.enrollment_start == 'Foo'` in either case.

I understand that the underlying `modulestore` api calls might take a `fields` dictionary, but I think you should construct that in this factory constructor, rather than expecting the user of the factory to build it.