MDL-40343 forum: indent less when mobile, nested

Changes the indenting of forum replies to be relative to the width of
the parent container, so the indent decreases as threads get nested
deeper. Also reduces the indent size automatically for smaller screen
sizes.
MDL-46088 Impossible to click on Atto in a Quiz in 'Secure' mode.
MDL-46088 Quiz: Prevent alert when clicking in editor in secure popup
MDL-46088 quiz secure window: further Atto JS fixes.
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-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-33939 gradingform_guide: use correct max grade for scales.
MDL-47499 tasks: Scheduled tasks custom schedule is reset on upgrade.

Add a unit test for reset_scheduled_tasks_for_component and make sure it doesn't clear
customised schedules for existing tasks.
MDL-47632 calendar: Fixed iCal link going blue after visiting it
MDL-30358 forms: strict validation is too strict
MDL-47704 Grades: Fix for set_usedinaggregation

Used in aggregation was not resetting previously set values
when recalculating an aggregation. This meant that items no longer
in the aggregation, were displayed with stale weights in the user report.
MDL-36987 auth_manual: fix config for field locking

Thanks to Sergey for the patch
MDL-46133 tool_monitor: added event cleanup task
MDL-46133 tool_monitor: added unit tests
MDL-47664 phpunit: Do not use sequence number changes for Oracle

When resetting a sequence number, we call change_database_structure()
which in turns clears the MUC cache for databasemeta. This cache contains
information about the table, columns, etc.

After the cache is cleared, it must be re-filled, and it was discovered
that the get_columns() code which fills this cache can take a particularly
long time. Given that this is called for every table in Moodle, this can
add up to a significant period, and this is done on a per-testsuite basis.

On my SSD install this was taking approximately 40 seconds on each re-fill
of the cache.
MDL-47738 gradereport_history: User selector handles broke with 0 user

It was impossible to reopen the dialogue when the last search result
did not return any user.
MDL-38172 Lesson: Additional Info not displayed at end of lesson
MDL-47728 tool_monitor: added capability check before displaying link