* Add add_session webservice function skeleton.
* Implement add_session.
* Refactor add_session to return created session id.
* Implement add_attendance
* Minor improvements to add_session.
* Fix add_attendance and add_session.
* Implement remove_session.
* Add params and context validation.
* Implement remove_attendance.
* Missing permissions check for get_session.
* Add coverage for remove_attendance.
* Refactor unittest and add coverage for add_attendance.
* Set default grade if not specified.
* Add test coverage for add_session and remove_session.
* Add basic validation to all remaining methods.
* Rename new WS functions to match Moodle naming convention.
* Style changes to address CI test outcomes.
Ruslan Kabalin