Add an attribute to IfcWorkSchedule that defines the TaskConstraintPriority

Various scheduling tools have different logic in task time calculation. In some tools, the task that has the AsLateAsPossible constraint set will push all successor tasks that have AsSoonAsPossible constraint.
In order to define whether the task with AsLateAsPossible constraint is able to push all successor tasks that have AsSoonAsPossible constraints or not it’s needed to introduce TaskConstraintPriorotyEnum to the IfcWorkSchedule. The enum should contain the following values: AsLateAsPossible and AsSoonAsPossible.