MDL-47011 core_grade: added naive natural weight calculation to gradebook
MDL-47011 core_grade: added the ability to override grade_item weight
MDL-46966 core_grade: altered the default value of grade_aggregations_visible so only natural is on by default
MDL-47011 core_grade: added ability to un-override grade_item weight
Merge branch 'MDL-27011_natural2' of https://github.com/andyjdavis/moodle into MDL-46576-master