We don't rely anymore on computerized dates for timing. It was leading
to incorrect time tracking at heavy server loads. We now consider that
the temporal context has to be provided from the outside. This is the
most valid solution.

The next step is to integrate setTime to the methods of
AssessmentTestSession and AssessmentItemSession to make the API more
efficient and intuitive.

We also need to remove all references to the 'acceptableLatency' concept
which is not valid anymore in this context.