openolat#124: filter deleted files in the getNewest function used by the folder peek preview controller

openolat#123: make the invalidateOlatCourse call async as we do not use the response and the invalidation can take some time

openolat#99: do explicitly set the picture and video elements to visible as the delete button can't be seen by default

openolat#34: do not show any dropdown in the create course controller when the sismanager is disabled

openolat#86: fix getParticipantRepositoryEntry_forAll test to check a user can't see entries it's not a member of

openolat#86: removed problematic query condition that makes no sense here and turns out to allow non members to see all open courses in the 'my courses' portlet