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-47572 libraries: modify unittest to avoid random timing fail

Thanks to Nigel Cunningham
MDL-47583 tinymce_managefiles: correctly decode filename
MDL-47583 atto_managefiles: correctly decode filename
MDL-47585 stats: fixed incorrect user dropdown
MDL-44548 mod_scorm: force an external sync to check for updated files.
MDL-47594 core_accesslib: removed three useless lines of code
MDL-47613 wiki: allow searching several words

Thanks to Sandeep B for suggested solution
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-47631 report_participation: fixed filtering by letter
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-47646 CURL redirect unit test: handle broken servers
MDL-38732 gradereport_grader: Handle simultaneous graders
MDL-47667 profile unit tests: don't assume none by default.

E.g. if an add-on creates a user profile field on install, the test was
failing.
Merge branch 'MDL-38732-27' of git://github.com/FMCorz/moodle into MOODLE_27_STABLE
MDL-47629 quiz review: display cloze feedback on top of "Check" button
MDL-30358 forms: strict validation is too strict
MDL-38732 gradereport_grader: Undefined variable in unit tests