Add notion of study modules

What needs to be modeled?

A model of a generic study module. This would loosely connect the now existing SCCourseOfStudies with the SCAcademicEvent. Interdependence of the study modules should also be modeled.

Why is a new model necessary?

Modelling a study module enables us to group SCAcademicEvents to match dependencies for completing a course of studies (beyond the lecture directory)

Dependencies, issues, features that need to be resolved beforehand

1. Model of representing grading