Author: Damyon Wiese
MDL-43985 Assign: Allow teachers to skip notifying students about grade update.
backport of MDL-33600
http://git.moodle.org/gw?p=moodle.git;a=commit;h=941f4597b0f2b80fac5b9094013ac624806d520e
http://github.com/moodle/moodle/commit/941f4597b0f2b80fac5b9094013ac624806d520e
+ 2.6 en [sendstudentnotifications,mod_assign]
+ 2.6 en [sendstudentnotifications_help,mod_assign]