MDL-46302 correct atto img float right

Correct the atto image "float right" margin CSS
MDL-46552 session: add support for multiple servers in memcached session driver
MDL-46315 themes: Fixed display inconsistancy with help modals
MDL-46643 calendar: improved tab order of calendar detail pages
MDL-46470 bootstrapbase: support linkedwhenselected attribute for tabs
MDL-44015: EditPDF scrolls instead of drawing on iOS
MDL-46697 gradebook: Only count active users when needed (and only id)

The code only needs the id column to perform its count. On courses with a lot of users
fetching the whole user record for them all easily adds up to several hundred MB of
memory.
MDL-46676 profilefield_datetime: Use moodle time API
MDL-46600 core_grades: made it explicit in the error message that a failed grade import means nothing was imported.
MDL-21042 report_security: don't display warning for riskbackup unnecessarily
MDL-46681 qtype_multichoice: disabled unused options

For questions set to 'One answer only', the 'Clear incorrect responses'
and 'Show the number of correct responses' hint options make not sense,
and are not used. Hence we disableIf them.
MDL-46480 fix get_htmlelement_size() to deal with hidden or non-block elements
MDL-45759 javascript: Handle setting of the confirm button fields post-init
MDL-46718: Return user to last accessed page when quick grading
MDL-46496 libraries: Add additional tests for jquery and jqueryUI

The additional tests add a clear example of the use of jquery UI images in
addition to working JavaScript.
MDL-30668 gradereport_grader: split user preferences into individual courses

This solves the DB exception when users were trying to insert very large string in DB
MDL-46688 weblib: improve the highlight function.

Thanks to Joseph Baxter for suggesting some of the test cases.
MDL-46308 qformat_xml: fix import of broken calculated questions.

Questions like this should not exist, of course. But they do, so we
should avoid generating errors in this case.
MDL-46748 MathJax filter: Make misconfigured mathjax url less "fatal" for Atto.
MDL-46748 MathJax filter: Update setting default for https cdn url.