Fix issue with service.save for adding courses so that there is no chance of misusing this or accidentally creating duplicate course instances.

[chrxr]

The CourseService.save method is specifically set up to handle creating new Courses, but the repository.save method will update a course if the data-to-be-saved includes an id. We should:

1. Rename the CourseService.save method to something more descriptive, e.g. CourseService.createNewCourse.
2. Instead of using repository.save, use repository.insert, so that it does not update existing.