Changed models:
  - Choice now contains a count to reflect number of credits desired
  - Courses now have an optional specialization; Courses are associated
    with Lectures via LectureCredits
  - Lecture now has a description; Lectures are now associated with
    Courses via LectureCredits
  - Lectures have a text-field for lecturer/teacher
  - Preferences is associated with a Choice
  - Choices are associated with the Student