Notification of string changes

Author: Laurent David
MDL-73232 core_courseformat: Inform user when reaching section max
* Disable the Add new Section button when max has been reached
* It also grays out the (+) button between sections and display a tooltip
* When adding a new section via the (+) button between section
should add a section with the (+) (add) button disabled.


http://git.moodle.org/gw?p=moodle.git;a=commit;h=4fe100f16111a22778503c864cd6f0723c95878c
http://github.com/moodle/moodle/commit/4fe100f16111a22778503c864cd6f0723c95878c

+ 4.5 en [maxsectionaddmessage,core_courseformat]
+ 4.5 en [sectionaddmax,core_courseformat]