MDL-43960 assign: Add missing include

There was a report of mod_assign_save_grade webservice failing because of this.
I couldn't reproduce it, but grepping the code found one place where this include
should be added.
MDL-44573: Remove HTML tags in outputs column in offline grading worksheet
MDL-43985 Assign: Allow teachers to skip notifying students about grade update.

Backport of MDL-33600

Conflicts:
	mod/assign/locallib.php
MDL-41285 block_recent_activity: behat test for structural changes
MDL-44665 declare all quiz page types in the blocks UI.
Merge branch 'MDL-43960-25' of git://github.com/damyon/moodle into MOODLE_25_STABLE
Merge branch 'MDL-44665_25' of git://github.com/timhunt/moodle into MOODLE_25_STABLE
Merge branch 'mdl44573-moodle25' of git://github.com/tlock/moodle into MOODLE_25_STABLE
Merge branch 'wip-MDL-41285-m25' of git://github.com/marinaglancy/moodle into MOODLE_25_STABLE
Automatically generated installer lang files
Merge branch 'install_25_STABLE' of git://git.moodle.org/moodle-install into MOODLE_25_STABLE
weekly release 2.5.5+
MDL-38693 themes: removed z-indexes

Removed z-index styles from #dock across all themes; removed z-index style from #page-header in Overlay theme such that elements no longer occlude HTML editor.