no-jira: hardened my courses, groups, author env. against unconventional settings in sites administration

OO-984: if rating is disabled, don't filter by rating, don't retrieve my rating in the my course query

OO-990: only retrieve the roles once, use them for all access security control, retrieve the groups only if the roles coach, participant or waiting are there... to minimize the number of queries

OO-984: make comment and rating in course configurable, guest cannot book, rate or comment, fix access to members only resource by administrators