MDL-39959 events: Add event course_module_created
MDL-39959 events: Add event course_module_updated
MDL-39959 events: Add event course_module_deleted
MDL-39959 events: Replace legacy mod_created event with course_module_created event in course/dnduploadlib.php
MDL-39959 events: Fixup after review

Code style fixes.
Added validations for various fileds in module created, updated and deleted events.
Added more unit tests to test the added validations.