MDL-40054 events: changed instances_list to instance_list
MDL-40054 mod_lesson: replaced 'view all' add_to_log call with an event
MDL-40054 mod_lesson: replaced 'update grade' add_to_log call with an event
MDL-40054 mod_lesson: created function to generate a lesson module in PHPUnit
MDL-40054 mod_lesson: added PHPUnit test for the essay_grade_updated event
MDL-40054 mod_lesson: replaced 'grade view' add_to_log call with an event
MDL-40054 mod_lesson: added PHPUnit test for the essay_list_viewed event
MDL-40054 mod_lesson: replaced 'update highscores' add_to_log call with an event