Reruns/cms server side LMS-11016

This PR is an updated version of this old one: https://github.com/edx/edx-platform/pull/4573
oh, nvm.  I see the `.format` now in your suggestion.

The `.format` is done by the `CourseActionStateItemNotFoundError` class.  If we think it's confusing, I can remove the .format from the error class, and have each caller do the format instead.