Merge branch 'MDL-40731_headings' of https://github.com/andyjdavis/moodle

Conflicts:
	theme/bootstrapbase/style/moodle.css
MDL-41600: qformat_blackboard_six Fix test_import_match fail w/ddmatch

With qtype_ddmatch installed, the unit tests for qformat_blackboard_six
fail as they generate ddmatch questions instead of match ones. This
patch checks for ddmatch and changes the test to expect that instead if
its installed.
NOBUG: fixed whitespace
Merge branch 'MDL-41253-master' of git://github.com/sammarshallou/moodle
Merge branch 'wip-MDL-41556-master' of git://github.com/abgreeve/moodle
Merge branch 'MDL-41600' of git://github.com/aolley/moodle
Merge branch 'MDL-41626-master' of github.com:StudiUM/moodle
Merge branch 'wip-MDL-40347-master' of git://github.com/marinaglancy/moodle

Conflicts:
	theme/bootstrapbase/style/moodle.css
	theme/upgrade.txt
MDL-38661: Add keyboard support for expansion
MDL-38661 JavaScript: Ensure that ARIA tags are set when expanding/collapsing content
Merge branch 'MDL-41147-master' of git://github.com/sammarshallou/moodle
Merge branch 'MDL-38570-master' of https://github.com/timgus/moodle
Merge branch 'MDL-40735_lesson' of https://github.com/andyjdavis/moodle
Merge branch 'MDL-41451_master' of https://github.com/pauln/moodle
Merge branch 'MDL-28561_M26' of git://github.com/lazydaisy/moodle
MDL-41218 Object section_info calculates expensive data on demand only

Added phpdocs and unittests, removed unnecessary fields such as course and userid because they can be retrieved from modinfo
MDL-41192 course: Can not write to the read-only properties of cm_info
MDL-41192 course: Properties of cm_info are read-only and calculated on request

Also added phpdocs
MDL-41192 course: Added property-read cm_info::effectivegroupmode
MDL-41192 course: Added unittests for cm_info properties