MDL-47183: viewhiddenactivities should use the module context

Thanks to Paulo Matos for the forum part of this change.
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-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-47909 mod_forum: Respect user autosubscribe setting on post

Re-appropriate the forum autosubscribe setting as a discussion
autosubscribe setting.

The setting was no longer used after the per-discussion changes. The
original plan had been to remove this setting, but there is some benefit to
respecting it for discussion subscriptions instead.