Notification of string changes

Author: Thanh Le
MDL-35792 question preview: way to update options without restarting.
It is useful, and possible, to update the display options without
restarting the question. You now only have to restart if you are
changing the maximum mark or the behaviour.


http://git.moodle.org/gw?p=moodle.git;a=commit;h=83a23ea878e4a4aa4dccfcfe8441fd0072c0bfb5
http://github.com/moodle/moodle/commit/83a23ea878e4a4aa4dccfcfe8441fd0072c0bfb5

+ 2.4 en [attemptoptions,core_question]
+ 2.4 en [displayoptions,core_question]
+ 2.4 en [updatedisplayoptions,core_question]