Cut Nr. 8.
All tests pass.
Separated Event_scheduler into Event_queue and Event_scheduler.
Added new Event_scheduler_ng which is the new scheduler and is used
system-wide. Will be moved to the event_scheduler.cc in the future.
Using Event_timed in Event_queue as well as cloned during execution.
Next step is to have Event_worker_data which will be used during execution
and will take ::compile()/::execute() out of Event_timed.
This is the first cut of separating Event_scheduler in two
classes which are more specialized.
Inheritance was used to separate methods and member variables.
Still Event_scheduler is a child of Event_queue. This dependency
will be removed soon.