Author: Mihail Geshoski
MDL-75513 core_grades: Create trigger element for the group selector
Creates a renderer method and a template for the element that would
trigger the group selector.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=8b2f9b0386b504142ea5d2a155e0f89cf8bb90e0
http://github.com/moodle/moodle/commit/8b2f9b0386b504142ea5d2a155e0f89cf8bb90e0
+ 4.1 en [selectgroupsseparate,core]
+ 4.1 en [selectgroupsvisible,core]