Completed documentation for Unit.
Added corresponding constructor to SubAssessment.
Missed out stuff for javadoc.
There won't be any maxMark in the beginning.
Javadoc for SubAssessment done.
Formatting changes.
Javadoc edit.
Javadoc for Staff done.
Implemented forgotten setter method for subAssessmentID.
Formatting changes.
Remove unneeded imports.
Javadoc for Mark done.