Add the logs to the course tasks (both backup and restore).

Activity logs are added to backup by each activity backup (see backup_activity_logs_structure_step) step.

We need one new step, backup_course_logs_structure_step, executed by the course task, in charge of backup all the course logs not belonging to any activity.

Should be simple.

When available, restore will need to perform the opposite operation, if logs have been selected to be restored. This will be for sure, more complex, as far as it involves re-encoding a lot of information (course/module/user.... ids).