Author: Andrew Davis
MDL-46175 core_grading: updated grading related strings
http://git.moodle.org/gw?p=moodle.git;a=commit;h=e54e51931d3b87a792d9d6ebf2a1419fd237901b
http://github.com/moodle/moodle/commit/e54e51931d3b87a792d9d6ebf2a1419fd237901b
+ 2.8 en [aggregateonlygraded,core_grades]
+ 2.8 en [categoriesanditems,core_grades]
+ 2.8 en [categoriesedit,core_grades]
+ 2.8 en [edittree,core_grades]