The Type of IloShiftListObject allows you to define the behavior during the search
regarding the variables of concerned activities. The possible types are:
OnStart: Shifts only affect the start of the activity.
For instance, if the shift is the interval [a,b), then the
start of the activity must be strictly smaller than a or greater
than b.OnEnd: Shifts only affect the end of the activity.
For instance, if the shift is the interval [a,b), then the
end of the activity must be strictly smaller than a or greater
than b.OnOverlap: Shifts affect the whole activity.
That is, the activity cannot overlap shifts. For instance, if the shift
is the interval [a,b), then the end of the activity must be
strictly smaller than a, or the start must be greater than b.