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-41593 admin: use default setting if preventexecpath active

This resolves problems when installing Moodle
and addons when preventexecpath active.

Please note the admin_setting_configfile is still
incorrectly restricted - this will be resolved by
MDL-40949.
MDL-47585 stats: fixed incorrect user dropdown
MDL-47555 core_availability: Issue with page layout & grade restriction

* Set pagelayout before getting section info, otherwise conditional activity renderers will default to the default 'base' layout.
MDL-47612 gradereport_grader: Remove max-width for RTL

For some reason, Safari behaves incorrectly when dealing with RTL
content where the table has a max-width of 100%.
MDL-30358 forms: strict validation is too strict
MDL-36987 auth_manual: fix config for field locking

Thanks to Sergey for the patch
MDL-38065 gradebook: Fix issue with hidden categories breaking rowspan.

Hidden subcategories break the rowspan in the gradebook; this fix corrects
the calculation of the rowspan.
MDL-38172 Lesson: Additional Info not displayed at end of lesson
MDL-29873 Lesson: Essays not shown on grade page with SQL server
MDL-47684 mod: better validation of rating options
MDL-47752 grading: fixed bugs with the modgrade element
MDL-46499 navigation: better enrolled course limit

We now user $CFG->navcourselimit to limit the number of
courses shown in the navigation when browsing another users
full profile. Previously it showed all courses which caused
some slowdown.
MDL-47077 report_participation: fixed pagination in groups
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-47754 install: fix redirect loop
MDL-47760 grades: dim category name if hidden
Merge branch 'MDL-38065-fix-27' of git://github.com/jmarthaler/moodle into MOODLE_27_STABLE