All tasks begin on the project start date by default
One exception is the case where a dependency is set up.  There are
times, however, when a dependency doesn't exist, but the task must
start on, or no earlier than a specific date.  You can
specify these constraints in the start date dialog.
You can delete the constraint for the current task using
ActionsReset constraint, or for all the tasks by choosing
ActionsReset all constraints.
