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-46448 core_rating: now only formats rating aggregate if user can see it
MDL-46561 session: use full session validation in \core\session\manager::session_exists()
MDL-32917 calendar: Fix centering of calendar heading on IE10
MDL-45897 behat: fixed behat for my home page
MDL-46175 behat: Fixed lang changes in gradebook
Merge branch 'MDL-32917-master-1' of https://github.com/andrewnicols/moodle
Merge branch 'wip-mdl-46175' of https://github.com/rajeshtaneja/moodle
MDL-21042 report_security: don't display warning for riskbackup unnecessarily
MDL-46711 session: add support for multiple servers to memcache session driver

Includes proper definition of object properties which fixes handling of timout default.
Merge branch 'install_master' of https://git.in.moodle.com/amosbot/moodle-install
weekly release 2.8dev
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-45642 questions: add required index to question_attempts.

It is important to be able to tell which behaviours are in use, and
without this index, it requires a complete scan of this table, which can
be very big, to verify that a behaviour is unused.