DelayEvents(Milliseconds delay) had different semantics than
DelayEvents(Milliseconds delay, uint32 group).
The first method delayed the events only in the case the internal timer
already ticked at least for the amount of delay. In contrast the latter method
delayed events regardless of the internal timer value.
Use the latter semantics for DelayEvents(Milliseconds delay) as well which makes
the outcome more predictable. Adapt tests accordingly.
With the switch to std::chrono return type of GetTimeUntilEvent
we don't run into an overflow condition which happend with the previous
uint32 return value if the events scheduled execution time is in the past.
Test for this case.
