OO-1548: set configuration for the local query cache and timestamps based on the default configuration of the hibernate-infinispan library

OO-1546: hardened the remove method against unexpected case, identity not participant, don't remove the last user without check it...

OO-91: add more informations to the list of groups and assessed identities and fix some other issues

OO-991: implements relative dates for assignment, submission and solution due dates, enhance the reminders rules engine to support them

OO-1544: better check of the validity of the last history point used in the "close" method of the course tab