MDL-39020 phpunit: Rename incorrect filename

Rename externallib_tests.php to externallib_test.php
Fix failing unit tests
MDL-40386: Fix for updating timemodified field in book_chapters
MDL-40434 calculatedmulti multiple-response questions not randomised
MDL-39558 badges: Add backup/restore to course badges
MDL-39558 badges: Add backup/restore of manually awarded badges
MDL-39558 badges: Prevent backup of badges without user information
MDL-39986 badges: Show badge navigation to users with awardbadge capability

Also fixes an arror when a user with this capability tries to award a badge,
but their role is not among the criteria set up for a badge
MDL-40472: Clean all codechecker warnings on mod_assign
MDL-40376 Fix copy/paste typo
MDL-40308: Fix javascript for lti mod_form

It was toggling the state of the hidden input - not the checkbox.
weekly release 2.5+
MDL-36479 quiz regrade: use progress bar to prevent time-outs
MDL-40318 quiz intro comprising just an impage was not shown

Also, ensure that we don't output an empty box if there are no access
messages.
MDL-40443 setType notice in quiz reports.
MDL-40392 Navigation -> my courses listing tests

This introduces some behat tests to verify that
the display of enrolled courses in the navigation
block works as expected, both when a plain list
or a nested list is configured.

Personally I'm not happy with the way to select
expected text via css element. I'd love to see
something in an higher level like

I should see the text|link "xxxxx" in the "yyyy" "element"

with element being "block, header, footer, main...."

But that's another issue.
MDL-40499 Edit question from 1.9 backup breaks if images in subdirs
MDL-40512 SCORM: prevent undefined warning
MDL-40527 enrol meta: respect $CFG->courselistshortnames

Thanks to James Henestofel for working this out in MDL-37558. That issue
got complex, so I am just submitting this simple part of it for
integration.
MDL-40488 improve $CFG->admin docs
Moodle release 2.5.1