Allow HoD Assessment grades to be used in Tracking Manager

Currently only OAS grades entered by subject class teachers are available in Tracking Manager. Tracking needs to reference baselines like target grades, and where a set has multiple teachers it makes sense for the HoD to be entering a single target. Our target grades are therefore entered by our heads of department but these crucial data are unavailable in Tracking Manager, unless we import them as external data, which seems like a big omission to us.