normalize schedule so that gantt does not output different line if the same operator is reallocated to the same machine

CoreObjects to calculate queue level at the end of simulation. Also operators to ouput schedule even if empty

This reverts commit 19ecf7d2.

This reverts commit e4980345.

It runs two scenarios, one with the order and another one without.

If due date has an incorrect format it is better to fail than to hide
the error and produce wrong results.

http://docs.dhtmlx.com/gantt/desktop__configuring_time_scale.html#addingthesecondscales