(WIP) Class diagram transfer

A start at transferring content from the class diagram into code.  Focuses on School/Course/Klass/Educator/Student type models.  

@Dantemss I'd appreciate a once over of this PR if you have a chance.
Good catch re the validation.  Actually discovered this as an issue recently in Tutor 2.  I put in a TODO to add this validation.  Like I said above, klass and section listed separately here because section is optional, klass is not.