openolat#233: show a disclaimer when choosing to create a course with learning path node access type

Share the current request timestamp acrros window via the test session
controller, calculate the time left specifically with the request
timestamp as base (not the start time of the current question), forbid
setting a timestamp older than the current one

recordings

openolat#225: do only hide the open calendar form link instead of removing it (resulting in an error message)

Force the nick name to be unique with a DB constraint, with an issue
where the user name for the OLAT token is the auto generated identity
name after changing the password