MDL-47183: viewhiddenactivities should use the module context

Thanks to Paulo Matos for the forum part of this change.
MDL-47734 core: Do not set scrolltop on fixed dialogues

Fixed position dialogues use a different xy positioning than standard
dialogues so cannot use the scrollTop positioning method.
MDL-46215 mod_forum: Improve style of subscription state

With the implementation of per-discussion subscription, the current
discussion's subscription state must be shown.

Since this state belongs to the discussion rather than the forum, it
should be shown accordingly.  This change therefore includes the addition
of the discussion name as a heading on the page.
MDL-47676 core_grades: reset is hidden in menu, using proper step
Merge branch 'MDL-47734-master-fixes' of git://github.com/andrewnicols/moodle
Merge branch 'wip-mdl-47676-m' of https://github.com/rajeshtaneja/moodle
MDL-47839 core_grades: Minor styling improvements to setup/user report
Merge branch 'MDL-47839-master' of git://github.com/FMCorz/moodle
MDL-47559 user_menu: customusermenu setting
Merge branch 'MDL-46215-master' of git://github.com/andrewnicols/moodle
MDL-47585 stats: fixed incorrect user dropdown
Merge branch 'MDL-47183-master' of git://github.com/andrewnicols/moodle
Merge branch 'MDL-47559-master' of git://github.com/jethac/moodle
MDL-47183 post-integration fixes

* Fixed typo with context_module::instance
* Fixed use of $mod->get_context()
MDL-47559 User menu: version bump for new settings
MDL-47877 mod_forum: Correct subscription options for forums

Test was the wrong way around when checking subscription state.