Author: Cameron Ball
MDL-52522 grades: Add rescale grades option for grade categories.
When a grade category is overridden, it starts to behave like a regular grade item.
Therefore we need similar behaviour to what was implemented in MDL-48634.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=fa8e27b32b7481431e9c7800f5ba79a7f1088cbb
http://github.com/moodle/moodle/commit/fa8e27b32b7481431e9c7800f5ba79a7f1088cbb
+ 3.1 en [modgradecategorycantchangegradetypemsg,core_grades]
+ 3.1 en [modgradecategorycantchangegradetyporscalemsg,core_grades]
+ 3.1 en [modgradecategoryrescalegrades,core_grades]
+ 3.1 en [modgradecategoryrescalegrades_help,core_grades]