Author: Jonathon Fowler
MDL-44268 assign: add 'not submitted' and 'no marker' filter options
http://git.moodle.org/gw?p=moodle.git;a=commit;h=c80d59f269c3ad0a569781243652bcd3fdd449c0
http://github.com/moodle/moodle/commit/c80d59f269c3ad0a569781243652bcd3fdd449c0
+ 2.7 en [filternotsubmitted,mod_assign]
+ 2.7 en [markerfilternomarker,mod_assign]