StudentGrade does not extend SIFDataObject

[catrider]

StudentGrade does not extend SIFDataObject, which means that it's not possible to build an Event from it and report it to a Zone. According to the SIF spec, StudentGrade is a reportable SIF_Event, so I believe this needs to be fixed.

[joerghuber]

StudentGrade is defined in the US Specification and would need to be fixed in that branch of the Data Dictionary.