Author: Petr Škoda
MDL-35843 implement self enrolment expiry notification
http://git.moodle.org/gw?p=moodle.git;a=commit;h=8a486fdb7d9a214a5b49f0f3d16aeb512258666e
http://github.com/moodle/moodle/commit/8a486fdb7d9a214a5b49f0f3d16aeb512258666e
+ 2.4 en [expirymessageenrollersubject,enrol_self]
+ 2.4 en [expirymessageenrollerbody,enrol_self]
+ 2.4 en [expirymessageenrolledsubject,enrol_self]
+ 2.4 en [expirymessageenrolledbody,enrol_self]
+ 2.4 en [messageprovider:expiry_notification,enrol_self]