MDL-47183: viewhiddenactivities should use the module context

Thanks to Paulo Matos for the forum part of this change.
MDL-46712: Center EditPDF window on browser resize / zoom
MDL-47585 stats: fixed incorrect user dropdown
MDL-30358 forms: strict validation is too strict
MDL-47608 cachestore_mongo: fixed unit test error

If you configured your site to run mongo unit tests and had
the mongo extension and backend installed but did not have the
mongo service running you would get a fatal error when running
the unit tests.
That problem has been fixed by checking the mongo test instance
is ready before returning it.
MDL-46518 navigation: site glossaries now expand properly
MDL-47760 grades: dim category name if hidden
MDL-47780 core: corrected docs for get_user_capability_course()
MDL-47397 editor_atto: Properly close confirm dialogue in Behat test
MDL-47397 assignfeedback_editpdf: Copy stamps to other students in team

During a team submission the stamps were attached to the user that
was graded and not to the other users. This could lead to errors when
generating the PDF for each user.
MDL-47397 assignfeedback_editpdf: Tests use reliable way to annotate PDF

The drag and drop step did not work, so we moved to using the stamps
to annotate the PDF. They do not rely on drag&drop and produce the same
effects.
MDL-47804 events: calendar_event_updated needs to accept a timestart == 0
MDL-47690 web services: Fixed invalid return parameter type in mod_url
Merge branch 'MDL-47397-27' of git://github.com/FMCorz/moodle into MOODLE_27_STABLE
Merge branch '47608-27' of git://github.com/samhemelryk/moodle into MOODLE_27_STABLE
Merge branch 'MDL-47804_27' of git://github.com/aolley/moodle into MOODLE_27_STABLE
Merge branch '46518-27' of git://github.com/samhemelryk/moodle into MOODLE_27_STABLE
Merge branch 'wip-MDL-47760-m27' of git://github.com/marinaglancy/moodle into MOODLE_27_STABLE
Merge branch 'MDL-47780_m27' of https://github.com/markn86/moodle into MOODLE_27_STABLE
Merge branch 'MDL-46712-27' of git://github.com/jethac/moodle into MOODLE_27_STABLE