Author: Davo Smith
MDL-50647 group: add 'not in group' section to groups overview
Also adds 'No group' and 'No grouping' filters to the top of the page
http://git.moodle.org/gw?p=moodle.git;a=commit;h=294c4bb0db8147cf971c28d1ff6e68c915dea734
http://github.com/moodle/moodle/commit/294c4bb0db8147cf971c28d1ff6e68c915dea734
+ 3.0 en [nogroup,core_group]
+ 3.0 en [notingrouplist,core_group]