OO-2479: reduce overhead everywhere, optimized and simplified query to count the participants of a group, bypass reloading the group set of identities, bypass reloading the base group of business group...

OO-2371: check if the participant is in group of a enrollment element before allowing it to leave the course

OO-2402. don't try to launch a resource if there is nothing to launch, hardened the authentication dispatcher to accept manipulated urls and redirect them to the current page

OO-2212: send 403 if the request to mapper /m/ has not a valid session id, this is a workaround for iOS 10 video bug

OO-2288: clean up the reference of the test if the course is corrupt, if the course node doesn't exist in run structure and in editor model

OO-2217: update the url converter to make absolute / url, but cut the mapper url of images and video...