MDL-36002 core: Make drag and drop keyboard friendly

This change adds keyboard support to core drag and drop.

Selecting a grab handle and hitting enter (or space) will
open a menu of possible drop targets and allow you to choose one.

The only other UI change this implies is we need to show the grab
for blocks.
MDL-36005 formslib: Move the help icons out of the form labels for accessibility.
MDL-36005 formslib: Version bump for css changes
MDL-36002 dragdrop: focus fix and exception catching

This sets the focus correctly after a cancel or drop event.
It also catches exceptions from the lock/unlock functions.
MDL-36002 dragdrop: Add simulated event for keyboard drag drop.

This is to prevent any accidental state change in Y.DD.DDM.
MDL-40852 behat: Wrong URLs detection
MDL-40673 behat: Data generator for permission overrides
MDL-40673 behat: New scenario for permission overrides
MDL-41050 Progress bar: Width parameter does not work
MDL-40711 blogs: Replace blog_entry_deleted with events2
MDL-40711 events: Resolve conflicts with MDL-41000 and add phpdocs
MDL-41068 profile: Repair profiling after box API change

The box API was used with an extra incorrect parameter
in the profiling code.  It worked without issue until
the introduction of error checking in MDL-40842.  It
has failed since then.
MDL-41045 course_add_cm_to_section should not test for sections unless necessary
MDL-22236 Webservice file upload - Allow webservice file uploads direct to a draft filearea.

Via post to /webservice/upload.php
MDL-22236 user webservice: add_user_private_files

Add webservice for adding files to user private files.
MDL-22236 webservice : Remove filearea restrictions on user draft areas.

It does not make sense to apply restrictions to the size of a users draft areas
so this is only checked if uploading direct to user private files.
MDL-30001 WEBCT Import does not work for 2.0
MDL-41019 refactor string managers to new core_ classes
MDL-41073 do not delete plugininfo caches when testing if upgrade necessary

This should help with performance for all users when admin is logged in
because these caches need to be purged only after upgrade.
MDL-27655 improve purge all caches.

If you click the link in the page footer, then it will reliably
redirect you back to the page you were on after purging the caches.

If you go to the purge all caches page in the admin menu, it shows you a
purge button, with no cancel button. Clicking the button purges the
caches and takes you back to the page with the button.