MDL-45359 JS: Only change mask zIndex on modal dialogues

When dealing with a non-modal dialogue within a modal dialogue, we should
not update the z-index of the underyling maskNode as it does not belong to
this dialogue.
MDL-43319 phpdoc: fix too much ham consumption by developers
MDL-45382 atto_link: Missing context when finding anchors
MDL-45342 book: Automate MDLQA-2423 - A teacher can create book chapters and subchapters
MDL-44174 theme_clean: Updating information in readme file
MDL-34904 lti: Fix notice while using lti in frontpage
MDL-45290 rubric: visual fixups

Fixed up visual issues with rubric editor on Clean.
MDL-45127 mod_lesson: Updated question edit screen with more help text.

Unless the custom scores is selected in the lesson settings the score section
in the question settings will be disabled. A help link has been added with
a description similar to this one.
MDL-45127 mod_lesson: Fixed reviewing lesson answers changing the lesson grade.
MDL-45127 mod_lesson: Behat test for reviewing a lesson.
MDL-45231 theme_clean: default navbar to absolute when running behat
Merge branch 'wip-MDL-45127-master' of git://github.com/abgreeve/moodle
Merge branch 'MDL-45382-master' of git://github.com/FMCorz/moodle
Merge branch 'MDL-45290-master' of git://github.com/jethac/moodle
MDL-44224 atto_indent: converts blockquotes to div indents
MDL-44224: outdent plugin - handle divs that have been silently switched for ps

Also - fix a shifter warning.
MDL-44972 Atto: Focus on the first input field in forms in dialogues.
MDL-45357 events: changed event descriptions to ensure consistency in core
Merge branch 'MDL-45357_master' of git://github.com/markn86/moodle
MDL-44972 Atto dialogues: Change M.core.dialogue attribute name to "focusOnShowSelector"

And some minor cleanups.