Notification of string changes

Author: ferranrecio
MDL-80191 backup: add subsections to backup form
The patch adds two new levels to the backup form structure: subsection
(a delegated section which parent is a course module) and subactivity
(an activity inside a subsection). Those new elements are displayed as a
inner section below the parent activitiy.

For now the UI is the same as a regular section but future issues will
define how the UX should be. The new two levels have their own classes
to represents settings and have extra dependencies.


http://git.moodle.org/gw?p=moodle.git;a=commit;h=c997f91db6c427fe251b49214c8cbbdd7339940e
http://github.com/moodle/moodle/commit/c997f91db6c427fe251b49214c8cbbdd7339940e

+ 4.5 en [subsectioncontent,core_backup]