MDL-45290 rubric: visual fixups

Fixed up visual issues with rubric editor on Clean.
MDL-45127 mod_lesson: Updated question edit screen with more help text.

Unless the custom scores is selected in the lesson settings the score section
in the question settings will be disabled. A help link has been added with
a description similar to this one.
MDL-45127 mod_lesson: Fixed reviewing lesson answers changing the lesson grade.
MDL-45127 mod_lesson: Behat test for reviewing a lesson.
Merge branch 'wip-MDL-45127-26' of git://github.com/abgreeve/moodle into MOODLE_26_STABLE
Merge branch 'MDL-45290-26' of git://github.com/jethac/moodle into MOODLE_26_STABLE