Change the way the impacted tasks are calculated

[lfasani]

When updating a task, impacted tasks are also updated.
Tasks are impacted because of:

• dependency link
• parent link
• internal constraint

Currently according to the calculation option, the task can have its effort changed during the update.
For example for a START_END or START_END task, with a dependency on END, the effort is changed if END is changed

Proposal:
All impacted tasks should have their effort kept unchanged whatever the calculation option
That means that a constraining task boundary can be changed during update.
The dependency link is stronger than the internal constraint