MDL-42476 report_progress: don't browser sniff for SVG support

Use feature detection, its more robust and better practice.
MDL-42318 coursecat: do not allow to sort if there are invisible children
MDL-42318 coursecat: show correct courses count

courses count should exclude courses that are not visible to the current user
MDL-42613 core_group: removed unnecessary table row when there is no group description or picture
MDL-42385 behat: New test to cover MDL-38661

Also refactoring set site settings step
as it has problems to deal with multiple-field
settings.
MDL-42318 coursecat: in unittests re-request category from DB after generating courses
MDL-42602 remove incorrect snapshot from \core\event\user_loggedin

* all snapshots in events should match the DB data
* the snapshot from user table will not be necessary most probably
MDL-42701 Bump all versions near 2.6 release
MDL-42701 Bump main version to observe all deps
MDL-42300 course: improved category re-sort controls.

* The top action now works on top level categories and has
  a better title.
* Each category has its own resort actions now.
MDL-42629 course: improved wording on move course dialogue
MDL-42629 course: tweaks CSS for management interface

* Removed grey background from checkboxes and bulk actions.
* Removed blue colouring on subheadings.
* Changed greys to the clean theme greys
MDL-42629 course: renamed re-sort to sort
MDL-42629 course: fixed up create category management actions
MDL-42629 actionmenu: alt and title on icon removed if the same as text being displayed
MDL-42629 course: changed sub category to subcategory
MDL-42629 course: moving a course now updates counts and pagination totals
MDL-42629 course: changed new course to create new course
MDL-42629 course: set a better management page title
MDL-42629 course: management resorting improvements