weekly release 2.4.4+
MDL-40264 fix essay handling of zero-string response

Fixes an inappropriate behavior of the is_complete_response() function
for the Essay question type, which caused the string "0" to be
inappropriately marked as an incomplete response.

Also adds a set of unit tests for the Essay question type's
is_complete_response.
MDL-34610 remove legacy IE CSS. It breaks form layout
MDL-38631 Fixed faulty add_category call, introduced in 758103
MDL-38631 link categories in My courses only when needed
MDL-40255 theme_boxxie/theme_formfactor: Added block-region class to layout files to enable dnd file uploader to work.
MDL-38376 mod_assign: Feedback displayed when Grade set to hidden
Merge branch 'MDL-28124_M24' of git://github.com/lazydaisy/moodle into MOODLE_24_STABLE
Merge branch 'wip-MDL-38347-stable24' of git://github.com/phalacee/moodle into MOODLE_24_STABLE
MDL-38347 fixed whitespace
Merge branch 'MDL-39280-24' of git://github.com/FMCorz/moodle into MOODLE_24_STABLE
Merge branch 'MDL-39760-MOODLE_24_STABLE' of https://github.com/lucisgit/moodle into MOODLE_24_STABLE

Conflicts:
	mod/assign/locallib.php
MDL-39044 - Course Completion - Replaceing strtolower with multibyte safe textlib::strtolower

Conflicts:
	blocks/completionstatus/details.php
MDL-40250 phpunit: Add unit tests for core_files_external::upload()
MDL-40258: Fixed invalid json string error in file-picker
MDL-40200 Administration: Return the invalid user message and stop there

To avoid adding duplicate code, 'invalid user' and 'user deleted' checks
have been merged together.
Merge branch 'MDL-40255_M24' of git://github.com/lazydaisy/moodle into MOODLE_24_STABLE
Merge branch 'MDL-34610_24' of git://github.com/timhunt/moodle into MOODLE_24_STABLE
Merge branch 'MDL-40264-m24-essay-zero' of git://github.com/ktemkin/moodle into MOODLE_24_STABLE
Automatically generated installer lang files