LDEV-2173 Adding in an averageTime and an averageMark parameter to the abstract GradeBookGridRow class as it makes sense for all views to have these parameters
LDEV-2187 Put time taken for activities and lessons in gradebook.Fixing up LearnerProgress.java so it stores both finish time and start time for all completed activities
LDEV-2173 Standardising sorting and searching for GradeBookGridRows, now all can sort on name, id, mark and timeTaken (common properties for all types) and all can search on name
LDEV-2173 Standardising sorting and searching for GradeBookGridRows, now all can sort on name, id, mark and timeTaken (common properties for all types) and all can search on name
