MDL-40343 forum: indent less when mobile, nested

Changes the indenting of forum replies to be relative to the width of
the parent container, so the indent decreases as threads get nested
deeper. Also reduces the indent size automatically for smaller screen
sizes.
MDL-46219 assignment: delete files when resetting assign activities
MDL-47569 backup: Escape section summary for XML

This was causing the parsing of the XML
to fail because things like & were not
escaped.
MDL-47569 backup: Do not close questions tag if never opened

This can happen when restoring quizzes that
do not have any questions.
MDL-33939 gradingform_guide: use correct max grade for scales.
MDL-36987 auth_manual: fix config for field locking

Thanks to Sergey for the patch
MDL-29873 Lesson: Essays not shown on grade page with SQL server
MDL-47755 badges: Fix internal message output

Signed-off-by: Yuliya Bozhko <yuliya.bozhko@totaralms.com>
MDL-47805 tool_monitor: More info in adhoc task
MDL-47647 lib: Fix message unit test failure.

Messaging unit tests on Windows were failing because
of a comparison between two file paths. Part of the
path would have a forward slash instead of a backslash
and so would fail.
MDL-47898 mod_quiz: Correct path when checking content_editable

Addresses a number of issues when using the text editor in a quiz using
secure mode.
MDL-47916 web services: Fixed invalid returned value type
MDL-47918 mod_forum: Unsubscribe all - remove discussion subscriptions
MDL-47227 admin: Fix user bulk selection over 1000
MDL-47919 tool_monitor: adjustments to behat tests
MDL-47368 Edit quiz: page should not reload so often

The approach is that we have a new JavaScript function
M.mod_quiz.resource_toolbox.reorganise_edit_page which, after a ajax
action, fixes up everything like page breaks, page and question numbers,
that might now be wrong.

We call that function instead of reloading the page.

Also, there are a lot more Behat tests to verify this works correctly.

AMOS BEGIN
 MOV [joinpages,mod_quiz],[removepagebreak,mod_quiz]
 MOV [splitpages,mod_quiz],[addpagebreak,mod_quiz]
AMOS END
MDL-47368 core JS: dragdrop click move fills the dom with divs

Every time you click the move icon, it builds a new dialogue with a list
of drop targets, but it never discards the old ones. Not only does this
fill the DOM with junk, but it also causes Behat tests to fail, since
the old dialogues come first, and are hidden, but contain links with the
same text that you are trying to click.
MDL-47368 quiz editing: fix icon url generation.
MDL-40949 admin: Fix $CFG->preventexecpath hints

This setting restricts all local paths, not just
executables.
Merge branch 'wip-MDL-36987-master' of git://github.com/marinaglancy/moodle