OO-3037: remove null in a first loop and sync in a second loop, add unit test which simulate the case

OO-3032: make the configuration of MathJax configurable and modify initialization script (patch D. Haag)

OO-3028: interpret start end with exactly 8640000 seconds, start without hour, minute and second as "all day" and fix the end accordingly to OpenOLAT behavior

OO-3028: interpret start end with exactly 8640000 seconds, start without hour, minute and second as "all day"