Author: Mihail Geshoski
MDL-75513 core_grades: Renderer for the prev/next user navigation
http://git.moodle.org/gw?p=moodle.git;a=commit;h=ba80b78119355edbbc51b476de0f6b763861e3af
http://github.com/moodle/moodle/commit/ba80b78119355edbbc51b476de0f6b763861e3af
+ 4.1 en [gotonextreport,gradereport_user]
+ 4.1 en [gotopreviousreport,gradereport_user]