This commit aims to improve duration field calculation
with subtask. So this commit :
- provides `subtask_planned_hours`as the total of planned our from
children tasks
- removes useless/unclear fields : delay_hours and total_hours
- makes progress computation independent from the stage (before,
progress
of task in fold stage was 100%)
- split the `hour_get` compute method into smaller ones in order to
improve
performances and code readability.
- makes 'progress' and subtask effective hours not including allocated
hours
Task: 38498