OO-2975: delete imported calendar after course, group and user deletion, implement a check every 10 runs to remove deprecated imported calendar, append the job to the scheduler

OO-2968: fill the title and short title independently of the assessment informations, add a fallback solution to the list to show the course title instead an empty title

OO-2935: remove unused link top for the full text search results, fix NPE if the context entry is null (it's the case if the user search for the name of the course element)