MDL-47197 core: Private files handler

This issue is a part of the MDL-47194 Task.
This issue is a part of the MDL-39707 Epic.
Merge branch 'MDL-31936-master-workshop-reset' of git://github.com/mudrd8mz/moodle
MDL-31936 workshop: version bump
Merge branch 'MDL-36460-master' of git://github.com/andrewnicols/moodle
Merge branch 'MDL-38106-master' of git://github.com/danpoltawski/moodle
MDL-46647 grades: Fix fetch_all_helper() towards cross-db

That helper, used to fetch information from DB by all the grade_object
chidren classes was not behaving properly handling TEXT/CLOB columns.

Instead of creating a property within every class listing the
existing columns, it seems to be a better solution to instrospect
the database metadata (cached) to ensure the correct SQL is generated
in every case.
Merge branch 'MDL-46284-master' of git://github.com/andrewnicols/moodle

Conflicts:
	lib/db/install.xml
	lib/db/upgrade.php
	version.php
Merge branch 'wip-MDL-36014-master' of git://github.com/marinaglancy/moodle

Conflicts:
	lib/db/install.xml
	lib/db/upgrade.php
	version.php
MDL-46647 core_grades: Adding tests for fetch_all_helper()
Merge branch 'wip-MDL-35618-master' of git://github.com/marinaglancy/moodle

Conflicts:
	theme/bootstrapbase/style/moodle.css
Merge branch 'MDL-32870' of git://github.com/jmvedrine/moodle
Merge branch '46481-28' of git://github.com/samhemelryk/moodle
Merge branch 'MDL-47518' of https://github.com/rlorenzo/moodle
MDL-47564 Availability: incorrect use of defined('PHP_UNIT')
MDL-45893 user_menu: responsive approach; fixed minor issues
Merge branch 'MDL-45893-master-v3' of git://github.com/jethac/moodle

Conflicts:
	theme/bootstrapbase/style/moodle.css
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.
Merge branch 'MDL-3714-master' of git://github.com/andrewnicols/moodle
MDL-3714 mod_forum: pre-integration clean up