CLONE - Section - Add CourseCharacteristics and GradeLevel to CourseOffering and Section entity (for v2)

Clone of DATASTD-1259 to consider same change for v2. Original description follows:

WI has a need to add GradeLevel to the Section entity.  It exists in StudentSchoolAssociation but not in Section.  It makes sense to have the GradeLevel part of Section also.  

Add it to the model, please.