Close ofter the hibernate session while deleting a learn ressource or a
files and directories

openolat#264: new role coursereader for read-only access to the list of courses, their configuration and the members

openolat#263: do add classes without o_icon prefix also to the surrounding div to be able to disable entries

Merge branch 'OpenOLAT_15.2' of ssh://srosse@office.frentix.com/home/srosse/repositories/OpenOLAT.git into OpenOLAT_15.2

Merge branch 'OpenOLAT_15.2' of ssh://srosse@office.frentix.com/home/srosse/repositories/OpenOLAT.git into OpenOLAT_15.2

And make delete task slightly more frightening