Author: Vadim Dvorovenko
MDL-45835 group: events for groupings assign/unassign
http://git.moodle.org/gw?p=moodle.git;a=commit;h=dd399f51abbab4819af19d6a522fac0f766aca40
http://github.com/moodle/moodle/commit/dd399f51abbab4819af19d6a522fac0f766aca40
+ 3.1 en [eventgroupinggroupassigned,core_group]
+ 3.1 en [eventgroupinggroupunassigned,core_group]