Author: Amaia Anabitarte
MDL-85852 course: Get groups to filter by in overview
http://git.moodle.org/gw?p=moodle.git;a=commit;h=2ae4ee14429cde3b9e02fc768ea55db0629e4dcc
http://github.com/moodle/moodle/commit/2ae4ee14429cde3b9e02fc768ea55db0629e4dcc
+ 5.1 en [overview_nogroups_error,core_course]
+ 5.1 en [overview_nogroups_title,core_course]